GIFT   OF 
Dean  Frank  E.    Probert 


Sold  by  Book  Department 
MINING  AND  SCIENTIFIC  PRESS 

42O  MARKET  STREET 
SAN    FRANCISCO 

Catalogue  of  Technical  Books  on  request 


.'r®;' 


WORKS   OF 
PROF.   WALTER   R.   CRANE 

PUBLISHED    BY 

JOHN    WILEY    &    SONS 


Gold  and  Silver 

Comprising  an  Economic  History  of  Mining  in 
the  United  States,  the  Geographical  and  Geo- 
logical Occurrence  of  the  Precious  Metals,  with 
their  Mineralogical  Associations,  History  and 
Description  of  Methods  of  Mining  and  Extrac- 
tion of  Values,  and  a  Detailed  Discussion  of  the 
Production  of  Gold  and  Silver  in  the  World  and 
the  United  States.  8vo,  x  +  727  pages,  illus- 
trated. Cloth,  $5.00  net. 

Index  of  Mining  Engineering  Literature 

Comprising  an  Index  of  Mining,  Metallurgical, 
Civil,  Mechanical,  Electrical,  and  Chemical  Engi- 
neering Subjects  as  Related  to  Mining  Engi- 
neering. 8vo,  xii  +  812  pages.  Cloth,  $4. 00  net. 
Morocco,  $5.00  net. 

Ore  Mining  Methods 

Comprising  descriptions  of  methods  of  support 
in  extraction  of  ore,  detailed  descriptions  of 
methods  of  stoping  and  mining  in  narrow  and 
wide  veins  and  bedded  and  massive  deposits,  in- 
cluding stull  and  square-set  mining,  filling  and 
caving  methods,  open-cut  work  and  a  discussion 
of  costs  of  stoping.  8vo,  viii  +  219  pages.  CO 
full-page  plates.  Cloth,  §3.00  net. 


ORE  MINING  METHODS 

COMPRISING 

DESCRIPTIONS  OF  METHODS  OF  SUPPORT  IN  EXTRAC- 
TION OF  ORE,  DETAILED  DESCRIPTIONS  OF  METHODS 
OF  STOPING  AND  MINING  IN  NARROW  AND  WIDE 
VEINS  AND  BEDDED  AND  MASSIVE  DEPOSITS 
INCLUDING     STULL     AND     SQUARE-SET 
MINING,     FILLING    AND     CAVING 
METHODS,     OPEN-CUT      WORK 
AND    A    DISCUSSION    OF 
COSTS    OF    STOPING 


BY 

WALTER    R.  CRANE,  PH.D. 

DEAN    OF   THE    SCHOOL   OF   MINES  AND    METALLURGY,   AND  PROFESSOR  OF 
MINING,  THE   PENNSYLVANIA   STATE  COLLEGE 


FIRST  EDITION 
FIRST    THOUSAND 


NEW   YORK 
JOHN    WILEY    &    SONS 

LONDON  :   CHAPMAN   &   HALL,  LIMITED 
IQIO 


GIFT  OB1 

FMNK  H 


COPYRIGHT  1910 

BY 

WALTER    R.   CRANE 


Stanbopc  ipress 

F.    H.   GILSON     COMPANY 
BOSTON.     U.S.A. 


cs 


PREFACE 

WHILE  much  has  been  written  with  regard  to  methods  of 
mining  ore  and  many  excellent  descriptions  of  the  methods 
employed  in  the  mines  of  the  United  States  and  abroad  are 
to  be  found  in  the  technical  press,  yet  there  is  no  work  in 
which  systematic  and  detailed  descriptions  of  the  various 
methods  are  to  be  found. 

With  this  thought  in  mind  the  writer  has  attempted  to 
prepare  a  work  on  ore  mining  methods  alone,  which  it  is 
hoped  may  prove  useful  to  both  the  student  and  the  prac- 
tical man  in  acquiring  a  knowledge  of  ore  mining  and  in 
comparing  methods.  That  the  work  may  be  of  the  most 
service,  the  descriptions  have  been  made  brief  and  many 
illustrations  employed  to  supplement  them.  Further,  the 
application  of  each  method  has  been  specifically  stated, 
together  with  the  advantages  and  disadvantages  of  its  use. 

The  classification  of  methods  followed  is  based  upon  size 
of  deposit,  rather  than  kind  of  mineral  or  metal  and  char- 
acter of  deposit,  which  seems  the  simplest  and  most  logical 
method  of  treatment.  The  idea  has  been  to  describe  only 
those  methods  which  have  proven  successful  not  only  in  one 
locality  but  several,  and  not  to  consider  proposed  methods 
nor  those  in  the  experimental  stage. 

In  order  to  verify  descriptions  and  to  study  methods  more 
in  detail  the  writer  has  visited  the  mines  in  which  practically 


iv  PREFACE 

all  of  the  methods  described  are  employed;  however,  personal 
inspection  has  been  confined  to  the  mines  of  the  United 
States. 

Special  acknowledgment  of  suggestions  and  advice  is  due 
to  Professors  Henry  S.  Munroe  and  Edwin  C.  Holden,  and 
the  large  number  of  mining  men  who  have  extended  many 
courtesies  to  the  writer  while  collecting  the  information 
upon  which  the  work  is  based. 

WALTER  R.  CRANE. 

THE  PENNSYLVANIA  STATE  COLLEGE 
SCHOOL  OF  MINES,  Jan.  i,  1910. 


CONTENTS 


CHAPTER  I 

Support  of  Workings 

PAGE 

INTRODUCTION i 

METHODS  or  SUPPORT 6 

PILLARS  OF  ORE  OR  WASTE;  TIMBER  AS  MINE  SUPPORT;  PROPS;  STULLS; 
CRIBS  OR  BULKHEADS;  SQUARE-SETS;  FILLINGS  OF  ORE  OR  WASTE;  SUPPORT 
BY  INDIRECT  MEANS;  RESUME  —  PILLARS,  PROPS  OR  POSTS,  STULLS,  CRIBS 
OR  BULKHEADS,  SQUARE-SETS,  FILLING,  CAVING 22 


CHAPTER  II 
Methods  of  Stoping  and  Handling  Ore  in  Stopes 

METHODS  OF  STOPING 23 

OVERHAND  STOPING;  UNDERHAND  STOPING;  COMBINED  STOPING;  BREAST 
STOPING;  SIDE  STOPING;  LONG  WALL  STOPING;  RESUING;  RESUME  OF  STOP- 
ING —  OVERHAND  STOPING,  UNDERHAND  STOPING,  BREAST  STOPING, 
OTHER  METHODS  OF  STOPING 43 

METHODS  OF  HANDLING  ORE  IN  STOPES 45 

CHAPTER  III 
Mining  in  Narrow  Veins  and  Bedded  Deposits 

INTRODUCTION 55 

MINING  BEDDED  DEPOSITS  BY  THE  USE  OF  PROPS 56 

IRON  MINES  OF  THE  BIRMINGHAM  DISTRICT,  ALABAMA 60 

MINING  MINERAL  VEINS  BY  THE  USE  OF  STULLS 60 

TONOPAH    MINE,  TONOPAH,  NEVADA;  COMBINATION  MINE,  GOLDFIELD, 

NEVADA;  HECLA  MINE,  BURKE,  IDAHO 72 

MINING  MINERAL  VEINS  BY  THE  USE  OF  SQUARE-SETS 72 

THE  BUNKER  HILL-SULLIVAN  MINE,  WARDNER,  IDAHO 77 

MINING  MINERAL  VEINS  BY  THE  USE  OF  FILLING 77 

THE  ZARUMA  MINE,  ZARUMA,  ECUADOR;  THE  ST.  LAWRENCE  MINE,  BUTTE, 

MONTANA;  THE  BALTIC  AND  TRIMOUNTAIN  MINES,  MICHIGAN 89 

MINING  BEDDED  DEPOSITS  BY  CAVING 89 

MERCUR  AND  GOLDEN  GATE  MINES,  MERCUR,  UTAH 94 

v 


vi  CONTENTS 

CHAPTER  IV 

Methods  of  Mining  in  Wide  Veins  and  Masses 

PAGE 

INTRODUCTION 95 

SHRINKAGE  STOPING  METHODS  OF  MINING 97 

THE  GOLD  PRINCE  MINE;  ANIMAS  FORKS,  COLORADO;  THE  ALASKA-TREAD- 
WELL  MINES,  DOUGLAS  ISLAND,  ALASKA 104 

SQUARE-SET  METHODS  OF  MINING 104 

THE   MINES  AT  ROSSLAND,   BRITISH    COLUMBIA;    THE    QUEEN    MINE, 

NEGAUNEE,  MICHIGAN no 

FILLING  METHODS no 

THE  BROKEN  HILL  MINES,  N.  S.  W.;  THE  HOMESTAKE  MINE,  LEAD,  SOUTH 

DAKOTA 131 

CAVING  METHODS 132 

IRON  DEPOSITS  OF  THE  LAKE  SUPERIOR  REGION;   THE  MINES  OF  BINGHAM 

CANYON,  UTAH;  THE  DIAMOND  MINES  OF  SOUTH  AFRICA 155 

CHAPTER  V 

Open-cut  Mining 

INTRODUCTION 156 

SURFACE  MINING  BY  HAND 158 

SURFACE  MINING  BY  SCRAPERS 163 

OPEN-CUT  MINING  BY  STEAM  SHOVEL 166 

THE  MILLING  METHOD 172 

CHAPTER  VI 

Cost  of  Stoping 

INTRODUCTION 183 

DETAILED  DISCUSSION  OF  COST  OF  STOPING 187 

COST  OF  STOPING  IN  VARIOUS  LOCALITIES , 193 

THE  COPPER  MINES  OF  KEWEENAW  POINT,  MICHIGAN;  THE  CRIPPLE  CREEK 
DISTRICT,  COLORADO;  THE  ALASKA-TREAD  WELL  MINES,  DOUGLAS  ISLAND, 
ALASKA;  THE  LEAD-SILVER  DISTRICT,  COZUR  D'ALENE,  IDAHO;  THE  GOLD- 
FIELD  CONSOLIDATED  MINES  COMPANY,  GOLDFIELD,  NEVADA;  THE  JOPLIN 
LEAD-ZINC  DISTRICT,  MISSOURI;  THE  WAR  EAGLE  MINE,  BRITISH  COLUMBIA  207 
COST  OF  SUPPORT  IN  STOPES 207 


LIST   OF   ILLUSTRATIONS 


FIGURE  PAGE 

Frontispiece 

1.  Corduroy  and  Filling  in  the  Comstock  Mines 2 

2.  Use  of  Square-Sets  and  Filling n 

3.  Forms  of  Square-set  Framing 14 

4.  Square-Sets  in  Large  Stope 16 

5.  Overhand  Stoping,  'Breaking-Through'  .  .  .  .' 26 

6.  Methods  of  Stoping  and  Handling  Ore.     A  Composite  Sketch 28 

(Correction.  —  Positions  of  'toe'  and  'heel'  reversed.) 

7.  An  1 8-inch  Stope  in  the  Rand  Mines,  South  Africa 30 

8.  Methods  of  Opening  and  Working  Deposits  by  Underhand  Stoping 33 

9.  Plan  of  Underhand  Stoping  Workings  in  Massive  Deposit 35 

10.  Loading  Cars  by  Chute,  Mohawk  Mine 47 

11.  Portion  of  Stope,  showing  Method  of  Handling  Soft  Ore .'. .  49 

12.  Use  of  Winged  Stulls  in  Handling  Ore 52 

13.  A  Chinaman  Chute  as  used  in  Australian  Mines 54 

14.  Plan  of  Iron  Mine,  Birmingham  District,  Alabama 58 

15.  Application  of  Stulls  to  Moderately  Wide  Veins ' 61 

16.  Use  of  Stulls  and  Stull-Levels  in  Mining  Moderately  Wide  Veins 65 

17.  Application  of  Stull-Sets  to  the  Mining  of  Medium-sized  Veins 69 

18.  Plan  of  Second  Floor  in  Stull-set  Method 71 

19.  Square-set  Mining  in  Horizontal  Floors 74 

20.  Square-set  Mining  in  Inclined  Floors 76 

21.  Overhand  Stoping  in  Inclined  Floors  or  Rill  Stoping 79 

22.  Elevation  and  Plan  of  Stopes.     Back-filling  Method 82 

23.  Baltic  and  Trimountain  Filling  Method 86 

24.  Caving  Method  in  Slightly  Inclined  Deposits 90 

25.  Plan  of  Caving  Method  in  Mercur  Mines,  Utah 93 

26.  Longitudinal  Section  through    Stope,  showing  Method    of  Working  by 

Shrinkage  Stoping 96 

27.  Vertical  Section  through  Stope  worked  by  Shrinkage  Method 99 

28.  Plan  of  Stopes  in  the  Alaska-Treadwell  Mines 102 

29.  Longitudinal  Section  through  Stopes  in  Alaska-Treadwell  Mines 105 

30.  Square-Sets  composed  of  Round  Timbers 107 

31.  Square-set  Mining  in  Massive  Deposit 109 

32.  Square-set  Mining  in  Broken  Hill  Mines,  N.  S.  W in 

33.  Plan  of  Square-set  Mining  in  Broken  Hill  Mines 114 

34.  Section  through  Lode.  Broken  Hill  Mines,  showing  Open-stope  Method  ...  116 

35.  Plan  of  Pillar-and-Stope  Method  in  Broken  Hill  Mines 118 

vii 


viii  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

36.  Back-filling  Method  used  in  Homestake  Mines 122 

37.  End  View  of  Stope  in  Homestake  Mine.     Back-filling  Method 124 

38.  Plan  of  Stopes  of  Back-filling  Method,  Homestake  Mines 127 

39.  Longitudinal  Section  through  Stopes  in  Homestake  Mines.    Back-filling 

Method 130 

40.  Section  through  Vein,  showing  Development  in  Top-slice  Method 131 

41.  Plan  and  Longitudinal  Section  of  Top-slice  Method 134 

42.  Section  through  Lode,  showing  Method  of  Development  in  Sub-drift  Method  137 

43.  Longitudinal  Section  and  Plan  of  Sub-drift  Method 140 

44.  Plan  of  Block  of  Bad  Ground  worked  by  Sub-drift  Method 142 

45.  Longitudinal  Section  through  Massive  Deposit  worked  by  Sub-drift  Caving 

Method 144 

46.  Plan  of  Portion  of  Sub-Level,  showing  Method  of  Caving  Ore  by  Raises .  .  .  147 

47.  Plan  of  Pipe  and  Method  of  Development  (in  Diamond  Mines) 149 

48.  Vertical  Section  through  Pipe,  showing  Method  of  Working  by  Galleries.  .  .  150 

49.  Section  through  Pipe,  showing  Method  of  Working  by  Caving 151 

50.  Elevations  and  Plans,  showing  Method  of  Opening  up  a  Stope 153 

51.  Sketch,  showing  Plan  of  Stopes  run  together 154 

52.  Vertical  Section,  showing  Stopes  in  Various  Stages  of  Working 155 

53.  Mining  Bank  of  Shale  by  Hand '. 159 

54.  Quarry,  showing  Bench  before  Blast 161 

55.  Quarry,  showing  Result  of  Blast 162 

56.  Stripping  Coal  by  Scrapers 164 

57.  Section  across  Bingham  Canyon,  showing  Beginning  of  Steam  Shovel  Work 

in  Stripping  Capping 167 

58.  Steam  Shovel  Mining  in  Soft  Iron  Ore  of  Birmingham  District,  Ala 170 

59.  Vertical  Section  through  Massive  Deposit  of  Iron  Ore,  showing  Method  of 

Development  and  Working  by  Milling  Method 176 


ORE  MINING  METHODS 


CHAPTER   I 
SUPPORT  OF   WORKINGS 

INTRODUCTION 

METHODS  of  mining  and  support  of  workings  are  so 
closely  related  that  the  discussion  of  one  necessitates  a 
more  or  less  detailed  treatment  of  the  other.  It  therefore 
seems  eminently  proper  and  even  necessary  to  preface  a 
work  of  this  character  with  a  brief  discussion  regarding  the 
elements  of  support.  A  description  of  the  elemental  units 
of  support,  such  as  pillars,  props,  cribs,  stulls  and  square- 
sets  will  not  therefore  be  out  of  place  in  this  connection. 
Further,  the  use  of  filling  is  considered,  as  it  is  rapidly 
becoming  an  important  factor  in  the  support  of  under- 
ground excavations;  caving  as  a  factor  in  support  is  also 
discussed. 

While  no  particular  knowledge  regarding  methods  of 
support  other  than  may  be  found  in  the  following  pages  is 
essential  to  a  full  and  complete  understanding  of  the  con- 
tents of  this  work,  yet  a  working  knowledge  of  support  of 
excavations  will  not  come  amiss,  and  such  knowledge  is 
assumed  to  be  possessed  by  the  intelligent  reader  of  this 
work. 


2  ORE  MINING  METHODS 

To  the  careful  observer  it  is  becoming  more  and  more 
evident  that  timber  cannot  be  relied  upon  to  support  mine 
workings  as  mining  is,  and  must  of  necessity  be,  carried  on 
to-day.  With  the  constantly  decreasing  value  of  the  mineral 
content  of  the  ores  of  many  mines  and  the  opening  up  of 
enormous  deposits  of  low-grade  ores,  the  demand  is  becom- 
ing more  urgent  for  decreased  costs  of  working  or  extracting 


FIG.  i. —  Corduroy  and  Filling  in  the  Comstock  Mines. 

the  ores.  Contemporaneously  with  this  general  trend  of 
affairs  has  occurred  a  scarcity,  in  many  localities,  of  a  suit- 
able supply  of  timber  at  reasonable  rates.  The  result  has 
been,  then,  that  with  no  other  available  material  at  hand 
that  was  cheaper,  methods  requiring  a  minimum  amount 
of  timber  were  resorted  to,  and  as  a  further  advancement 
filling  and  caving  methods  are  rapidly  coming  into  general 
use  and  are  supplanting  the  older  and  more  expensive 
methods  where  much  timber  is  used.  As  the  methods  of 


SUPPORT  OF  WORKINGS  3 

working  mineral  deposits  have  then  yielded  to  the  demands 
of  economy,  in  like  manner  the  old  type  of  conservative 
mine  superintendent  is  giving  way  to  the  ingenious,  ener- 
getic and  efficient  modern  mining  engineer,  whose  slogan  is 
"  increased  tonnage  at  decreased  costs." 

Further,  aside  from  the  question  of  economy  the  mining 
engineer  has  long  since  learned  that  timber  or  any  other 
similar  form  of  support  must  be  considered  as  temporary 
only  when  we  come  to  maintaining  openings  at  a  depth  of 
several  thousand  feet.  To  attempt  to  support  a  mountain 
by  timber  or  even  pillars  of  ore  or  rock  is  but  to  invite  in  the 
course  of  time  disastrous  caves  with  the  possible  resulting 
loss  of  life  and  property.  The  extremes  gone  to  in  an 
endeavor  to  hold  back  loose  or  swelling  ground  is  well 
illustrated  by  the  close-set  cribbing  or  corduroy  employed 
in  the  bonanza  days  on  the  Comstock  Lode  and  still  used 
there  in  isolated  places.  (See  Fig.  i.)  The  veritable  forest 
of  closely  placed  props  to  be  seen  in  many  of  our  metal 
mines,  and  the  stulls  of  three  or  four  feet  in  diameter  em- 
ployed in  the  lower  levels  of  the  deep  copper  mines  of 
Keweenaw  Point,  Michigan,  all  attest  the  ever-present  and 
constantly  growing  need  of  a  radical  change  in  methods  of 
procedure  in  supporting  workings  made  for  the  economic 
extraction  of  mineral. 

While  the  application  of  rock-filling  to  the  support  of 
mine  workings  is  by  no  means  recent  in  the  mines  of  the 
United  States,  yet  its  rapid  extension  to  a  majority  of  the 
metal  mining  districts,  irrespective  of  the  kind  of  metal 
mined,  has  taken  place  within  the  last  ten  years.  By  rock- 


4  ORE  MINING  METHODS 

filling,  as  referred  to  above,  is  meant  a  filling  of  waste,  the 
excavations  receiving  little  or  no  other  support  except  of 
the  most  temporary  character.  Filling  in  connection  with 
square-sets  has  been  used  extensively  in  the  mines  of  this 
country  ever  since  its  application  to  the  mines  of  the  Corn- 
stock  Lode. 

Aside  from  the  question  of  an  available  supply  of  suitable 
material  for  filling  there  are  certain  objections  to  its  use, 
some  of  which  are  so  serious  as  to  preclude  its  employment 
except  under  prescribed  and  limiting  conditions. 

Probably  the  principal  disadvantages  are  shrinkage  of  the 
mass  of  filling  and  a  tendency  to  become  ' quick'  and  flow. 
The  former  action  leads  to  movements  which  although 
gradual  are  nevertheless  pronounced  and  may  result  in 
serious  disarrangement  of  the  workings,  shafts,  levels,  etc., 
and  may  lead,  under  certain  conditions,  to  the  flooding  of 
the  workings.  However,  under  normal  conditions,  these 
disadvantages  may  be  insignificant  compared  with  the 
benefits  resulting  from  its  use.  The  latter  disadvantage 
while  always  present  is  accentuated  only  when  the  filling 
employed  is  mixed  with  a  certain  amount  of  earthy  or  clayey 
material  and  becomes  charged  or  saturated  with  water. 
Further,  the  practice,  often  a  necessity,  of  using  the  filling 
over  and  over  again  tends  to  render  it  less  suitable  for  the 
work  owing  to  the  constantly  increasing  proportion  of  fine 
material  produced  by  the  attrition  of  the  moving  mass  of 
filling,  when  drawn  from  one  part  of  the  workings  to  another, 
and  the  accumulation  of  gouge  and  muck  left  from  the  mining 
operations. 


SUPPORT  OF  WORKINGS  5 

It  is  not,  however,  so  much  the  seriousness  of  the  dis- 
advantages as  it  is  the  lack  of  control  of  the  actions  leading 
thereto.  It  may  be  said  without  hesitation  that,  where 
conditions  are  favorable,  such  as  a  moderately  strong  ore 
supporting  itself  sufficiently  well  to  permit  introducing  and 
spreading  the  filling  without  interference  with  temporary 
supports,  together  with  a  suitable  filling  and  plenty  of  it 
readily  available,  the  filling  methods  have  proved  and  are 
proving  amply  adequate.  When  such  general  conditions 
do  not  prevail  and  suitable  timber  at  reasonable  rates  is 
not  available,  some  other  method  not  dependent  upon  such 
factors  must  be  resorted  to.  The  caving  methods  might 
then  well  be  employed. 

Caving  is  confined  to  ore  bodies  of  considerable  size, 
especially  of  horizontal  extent,  and  to  ores  of  a  fairly  uni- 
form mineral  content,  its  application  being  gradually  ex- 
tended to  districts  where  other  methods  of  mining  have  long 
been  in  use.  Often  where  square-setting,  with  or  without 
filling,  was  formerly  exclusively  employed,  caving  has  now 
taken  its  place  wholly  or  in  part  or  a  combination  of  the  two 
is  resorted  to.  Caving  is  usually  employed  only  where 
other  methods  are  inapplicable  and  inadequate.  Its  use 
means  large-scale,  continuous  and  rapid  work,  with  a  con- 
sequently large  tonnage  and  small  expense  per  ton. 

Caving  is  not  synonymous  with  scant  use  of  timber;  on 
the  contrary  a  large  amount  of  timber  may  be  required  as 
when  the  sub-drift  system  is  used,  but  as  the  timber  is  for 
temporary  use  only,  being  often  of  inferior  quality  and  used 
in  the  rough,  the  expense  may  be  considerably  less  than  a 


6  ORE  MINING  METHODS 

more  permanent  method  of  support  where  less  timber  is 
employed.  What  timber  support  is  used  serves  mainly  for 
protection  to  the  miners  who  as  parts  of  an  intelligent 
system  are  directing  and  utilizing  the  tremendous  force  of 
the  superimposed  mass  of  loose  and  broken  rock  and  ore 
which  is  slowly  but  irresistibly  following  the  withdrawal  of 
the  ore  downward. 

METHODS  or  SUPPORT 

The  means  of  supporting  mine  workings  may  be  outlined 
as  follows: 

1.  Pillars  of  ore  or  waste  rock. 

2.  Timbering,  consisting  of  props,  stulls,  cribs  and  square- 
sets. 

3.  Fillings  of  ore  or  waste;  the  former  temporary,  the 
latter  permanent. 

4.  Support  by  indirect  means,  i.e.,  by  arching  the  work- 
ings and  by  caving  methods,  where  the  ore  to  be  mined  takes 
the  load  temporarily,  being  reenforced  by  timber. 

Pillars  of  Ore,  or  Waste  Rock.  —  Pillars  were  naturally 
first  employed  in  the  support  of  workings  underground,  and 
will  always  be  used  instead  of  artificial  support  except  when 
their  use  means  the  permanent  curtailment  of  the  output 
of  the  mine,  or  when  they  are  less  stable  and  durable  than 
other  available  supports. 

The  chief  objection  to  the  use  of  pillars,  aside  from  the 
loss  of  valuable  mineral,  is  that  it  is  difficult  to  ensure  their 
proper  formation  and  location.  To  secure  the  maximum 
benefit  of  supports  of  any  kind  requires  that  they  should  be 


SUPPORT  OF  WORKINGS  7 

symmetrically  and  systematically  placed,  a  thing  that  is  next 
to  impossible  to  obtain  in  the  case  of  pillars  underground. 
Either  there  will  be  ore  occurring  at  the  place  where  a  pillar 
should  logically  come  or  some  irregularity  of  or  in  the  deposit 
will  influence  a  change  in  location  and  result  in  a  serious 
irregularity  of  the  system  adopted.  In  like  manner  the 
shape  of  the  pillar  may  be  changed;  instead  of  a  square  or 
rectangular  section  with  ends  flaring  slightly  at  both  top  and 
bottom,  where  connection  is  made  with  the  hanging  and  foot 
walls,  the  sections  are  more  usually  roughly  round  or  ellipti- 
cal, while  the  general  appearance  resembles  an  hourglass. 

The  pernicious  habit  of  gradually  cutting  away  pillars 
to  secure  a  few  more  tons  of  ore  results  in  producing  most 
grotesque  shapes  and  an  alarming  condition  of  support. 
Pillars  standing  12  to  15  feet  high,  in  moderately  inclined 
deposits,  are  not  infrequently  reduced  from  a  diameter  of 
1 6  to  20  feet  at  the  top  and  bottom  to  4  and  often  3  feet  at 
the  middle,  and  in  certain  observed  instances  to  i  foot 
diameter  at  the  'waist  line.'  Such  pillars  soon  deteriorate 
under  the  enormous  weight  thrown  upon  them  and  show 
signs  of  distress  by  vertical  cracks  extending  from  top  to 
bottom.  The  caved  stopes  of  the  upper  levels  of  the  large 
copper  mines  of  the  Lake  Superior  region  bear  witness  to  the 
fact  that  inefficient  support  in  the  shape  of  ill-formed  pillars 
is  both  inadequate  and  futile. 

Pillars  are  named  according  to  the  position  they  occupy 
with  respect  to  the  stope;  those  at  the  top  of  the  stope 
are  known  as  'arch'  pillars,  those  next  to  the  shaft  are 
'shaft'  pillars,  while  those  occupying  various  positions  in 


8  ORE  MINING  METHODS 

the  stope  are  usually  known  as  'wall'  pillars.  A  special 
form  of  wall  pillar  is  the  so-called  '  dead-end,'  a  pillar  ex- 
tending the  whole  height  of  the  stope  and  spaced  at  inter- 
vals of  about  200  feet  along  the  stope.  (See  Fig.  6.) 

Timber  as  Mine  Support.  —  Timber  well  adapted  to  use 
in  underground  work  is  becoming  somewhat  scarce  in  many 
localities  in  the  United  States.  Oak  is  excellent  but  is 
rarely  used  owing  to  its  scarcity.  On  the  Pacific  coast  the 
cone-bearing  or  coniferous  trees  are  widely  used.  Of  the 
thirty-six  varieties  found  there  the  most  important  are: 
the  Oregon  pine,  spruce,  yellow  pine,  tamarack,  sugar  pine, 
pinion  or  bull  pine,  besides  several  varieties  of  fir  and  red- 
wood. In  Washington  and  many  of  the  Western  states 
the  Oregon  pine  is  extensively  used  for  both  mine  and 
surface  work  and  is  known  in  different  localities  by  various 
names,  such  as,  Douglas  fir,  Douglas  spruce,  yellow  fir  or 
red  fir,  while  in  the  parlance  of  the  lumbermen  it  is  known 
as  Oregon  pine  and  Puget  Sound  pine.  Yellow  pine  al- 
though of  no  great  durability  or  strength  is  widely  used. 

Fir  is  quite  strong,  as  is  pine  also,  the  softer  woods  having 
the  advantage  over  the  harder  in  that  they  crush  more 
readily,  thus  taking  up  the  load  more  uniformly. 

Props  or  posts  may  be  considered  as  the  principal  element 
in  mine  timbering,  being  employed  in  connection  with  nearly 
all  forms  of  timbering  under  certain  conditions.  Props  and 
posts  may  be  round  or  square  and  are  set  normal  to  the  roof 
and  floor  of  the  workings.  They  have  their  widest  range  of 
usefulness  in  flat  or  slightly  inclined  deposits  and  are  there- 
fore especially  applicable  to  bedded  deposits.  In  order  to 


SUPPORT   OF  WORKINGS 


increase  the  bearing  surface  caps  are  often  provided,  which 
consist  of  short  lengths  of  plank  placed  between  the  ends  of 
the  props  and  roof  or  floor. 

Stulls  while  performing  the  same  function  as  props  and 
posts  are  used  only  in  more  or  less  highly  inclined  deposits, 
having  their  widest  range  of  usefulness  in  narrow  veins, 
say  up  to  15  feet  in  width.  Stulls  are,  however,  used  in 
veins  of  35  to  40  feet  in  width,  and  for  inclinations  up  to 
90°,  or  the  vertical.  The  application  of  stulls  is  considerably 
different  from  that  of  props  owing  to  conditions  brought 
about  by  change  in  dip  of  the  deposit.  Like  the  prop  or 
post  the  stull  often  has  a  cap  used  with  it,  but  it  is  placed  at 
the  upper  end  only,  the  lower  end  being  set  into  a  notch  or 
'  hitch '  cut  into  the  lower  or  foot  wall  of  the  vein  and  wedged 
tight.  The  object  of  the  hitch  is  to  prevent  the  timber 
slipping  from  its  place.  Further,  stulls  are  not  set  normal  to 
the  walls  of  the  vein  but  in  such  a  position  that  their  devia- 
tion from  the  normal,  called  'angle  of  underlie,'  is  about 
one-fourth  that  of  the  angle  of  dip  of  the  deposit,  thus: 


Dip  of  Vein 

Angle  of  Underlie 
of  Stull 

Dip  of  Vein 

Angle  of  Underlie 
of  Stull 

10° 

•  :> 

40° 

10° 

20° 

5^ 

50° 

I2j° 

30° 

7i° 

60° 

15° 

The  reason  for  setting  stulls  at  an  angle  with  the  walls 
instead  of  normal  to  them  is  to  ensure  against  their  becom- 
ing loose  and  falling  out  of  place,  which  would  surely  result 
if  they  were  set  normal  and  a  movement  of  the  walls  should 


10  ORE   MINING   METHODS 

take  place.  When  set  at  an  angle  any  downward  move- 
ment of  the  hanging  wall  serves  only  to  set  the  stull  more 
firmly  in  the  hitch. 

Stulls  are  extensively  employed  at  the  foot  of  stopes  in 
veins  of  steep  or  moderately  steep  inclinations  and  serve 
both  as  a  protection  to  the  levels  and  as  a  support  for  the 
ore  or  waste  that  is  placed  upon  them.  Stulls  when  covered 
with  lagging  may  serve  as  platforms  upon  which  drills  may 
be  mounted  in  the  work  of  stoping.  In  steep  veins,  inter- 
mediate levels  or  floors  may  be  formed  at  intervals  of  15  or 
20  feet,  by  rows  of  stulls,  lagged  and  covered  with  ore  or 
waste,  the  stoping  of  the  ore  extending  horizontally  and 
vertically  from  the  level  so  formed  until  sufficient  room  is 
made  for  another  row  of  stulls  to  be  placed.  Waste-covered 
stulls  are  usually  designated  as  'waste-stulls.' 

It  is  often  necessary  to  reenforce  stulls,  which  is  usually 
done  by  placing  several  below  the  one  to  be  reenforced. 
The  auxiliary  stulls  may  be  placed  directly  below  or  grouped 
together  forming  the  so-called  'battery  of  timbers'  or  stulls. 
Still  another  modification  in  the  use  of  stulls  is  where  they 
are  used  in  conjunction  with  square-sets,  long  stulls  often 
being  employed  in  holding  the  square-sets  in  place  when  for 
certain  reasons  it  is  not  considered  necessary  or  desirable 
to  fill  the  stope  with  sets.  The  stulls  serve  in  reality  as 
elongated  caps  in  the  system  of  square-sets.  (See  Fig.  2.) 

Props  or  struts  and  stulls  are  occasionally  used  together, 
especially  when  long  stulls  are  necessary,  the  struts  being  set 
in  between  the  stulls  to  hold  them  in  place,  thus  steadying 
them  and  preventing  buckling. 


SUPPORT   OF  WORKINGS 


II 


12  ORE   MINING   METHODS 

Cribs  or  Bulkheads  are  usually  composed  of  damaged 
timber,  old  ties,  props  and  stulls,  put  together  in  pigsty 
fashion,  two  or  more  timbers  being  placed  parallel  one  with 
the  other  and  then  bound  together  by  other  timbers  laid 
across  their  ends  and  middle,  which  operation  is  continued 
until  the  roof  or  hanging  wall  is  reached,  when  they  are 
wedged  fast.  In  order  to  make  these  constructions  more 
stable  they  are  often  filled  with  waste.  Cribs  filled  with 
waste,  or  otherwise,  probably  have  their  widest  range  of 
usefulness  in  the  mining  of  coal,  but  are  often  employed  in 
wide  stopes  where  ordinary  methods  of  support  are  inade- 
quate and  where  a  certain  amount  of  room  for  mining  and 
handling  the  ore  is  available.  Cribs  in  combination  with 
filling,  being  built  in  the  stopes  during  the  extraction  of  the 
ore  and  then  buried  in  filling  when  the  stope  is  abandoned, 
give  added  strength  and  stability  to  the  filling. 

Square-Sets  have  been  very  extensively  employed  in  the 
metal  mines  of  the  United  States  and  are  still  used  to 
the  exclusion  of  other  methods  in  certain  districts.  While 
especially  applicable  to  wide  veins  of  moderately  steep  in- 
clinations, square-sets  are  often  used  in  veins  from  15  to  20 
feet  in  width. 

In  placing  square-sets  the  usual  practice  is  to  begin  at  the 
bottom  of  a  stope  and  lay  long  sill  timbers  which  are  regu- 
larly spaced  by  other  timbers,  thus  covering  the  floor  of  the 
open  stope  with  a  system  of  timbers  arranged  in  squares. 
Upon  these  timbers  are  erected  other  timbers  which  consist 
of  posts,  caps  and  girts  or  ties.  The  posts  are  placed  up- 
right at  the  intersection  of  the  sills  and  cross-pieces,  and  upon 


SUPPORT  OF  WORKINGS  13 

the  posts  are  placed  caps,  the  ends  of  which  rest  on  two 
adjacent  posts  in  a  direction  transverse  with  the  vein.  The 
girts  also  rest  upon  the  posts  but  run  longitudinally  with 
the  vein.  The  caps  and  girts  when  in  place  form  a  new  level 
or  floor,  and  by  successive  additions  of  posts,  caps  and  girts 
the  timber  support  can  be  kept  within  easy  reach  of  the  walls 
or  roof  of  the  stope.  In  like  manner  by  the  addition  of 
sills  the  sets  can  be  extended  indefinitely  in  either  direction 
along  the  vein  or  deposit.  A  platform  or  staging  as  well  as 
support  is  thus  provided  for  any  portion  of  the  roof  or  sides 
of  the  stope.  The  stopes  are  then  filled  with  a  cellular 
mass  of  timbering  perfectly  matched  together  and  symmet- 
rical in  all  directions. 

In  order  that  the  various  members  of  the  square-sets  may 
fit  together  and  be  in  perfect  alinement,  the  posts  standing 
vertically  and  the  caps  and  girts  lying  horizontally,  it  is 
necessary  that  they  be  cut  to  gauge,  and  the  ends  formed  so 
as  to  both  hold  the  members  in  place  and  provide  a  perfectly 
fitting  joint.  Further,  the  ends  of  the  different  timbers  are 
so  cut  that  the  largest  cross-sectional  area  is  opposed  to  the 
greatest  pressure,  as  in  the  case  of  the  caps  which  are  placed 
normal  to  the  walls.  While  there  are  a  large  number  of 
different  forms  of  joints  suitable  to  framing  both  sawed  and 
round  timber,  yet  the  details  given  in  Fig.  3  illustrate 
very  well  two  methods  of  framing  that  are  widely  used. 
Where  the  ground  is  particularly  heavy,  diagonal  braces 
are  placed  in  the  sets  and  in  line  with  the  greatest  pressure. 

The  length  of  the  posts  varies  largely  with  the  locality, 
but  as  a  rule  the  first  set  of  posts,  and  in  fact  the  posts  at  any 


ORE  MINING  METHODS 


SUPPORT  OF  WORKINGS  15 

level,  where  hauling  is  done  in  cars,  is  sufficiently  high  to 
permit  the  passage  of  men.  The  usual  length  of  posts  is 
6  to  8  feet  in  the  clear,  the  caps  and  girts  being  about  5  to 
6  and  4  to  6  feet  respectively. 

As  timber  became  more  difficult  to  secure  for  the  mines 
the  first  and  most  natural  expedient  was  to  modify  the  con- 
struction of  the  square-sets  by  using  rough  round  instead  of 
sawed  timber  and  the  employment  of  longer  posts.  Round 
timber  while  being  somewhat  more  difficult  to  frame  is  con- 
siderably stronger  than  the  sawed  forms.  Thus  the  result 
was  decreased  cost  of  framing  and  increased  strength. 

Increased  length  of  posts  also  decrease  the  cost  of  fram- 
ing, but  there  is  a  definite  limit  in  this  direction  if  strength 
and  rigidity  of  support  are  desiderata.  A  further  modifi- 
cation is  the  variation  in  size  of  the  different  members  of 
the  sets,  the  posts,  caps  and  girts  being  of  different  cross- 
sectional  dimension. 

A  drift  may  be  the  starting  point  of  square-set  timbering, 
which  is  extended  laterally  and  vertically  therefrom. 

Experience  has  shown  that  it  is  not  so  much  the  depth 
with  consequent  increase  in  pressure  as  the  strength  and 
firmness  of  the  walls  that  determines  the  usefulness  and 
safety  of  square-sets  as  support  for  workings.  This  was 
demonstrated  in  the  mines  of  the  Comstock  Lode,  where 
the  support  of  the  upper  workings  was  often  fully  as  difficult 
as  in  other  localities  at  greater  depth.  Further,  there  is  a 
limit  in  height  to  which  square-sets  can  be  used,  beyond 
which  the  timbers  will  crush  under  their  own  weight.  The 
limit  in  the  Homestake  mines,  South  Dakota,  ranges  be- 


i6 


ORE   MINING   METHODS 


SUPPORT  OF  WORKINGS  17 

tween  80  and  90  feet.  It  is  then  evident  that  when  square- 
sets  are  employed  the  height  of  the  stopes  should  not  exceed 
100  feet.  Use  of  square-sets  in  a  gold  mine  is  shown  in 
Fig.  4. 

From  the  standpoint  of  economy  the  use  of  square-sets 
is  hardly  warrantable,  although  there  are  instances  where 
owing  to  the  occurrence  of  cheap  timber  it  may  prove  to 
be  the  most  economical  method  that  can  be  employed. 

Fillings  of  Ore  or  Waste.  —  Filling  methods  have  been 
successfully  employed  for  many  years  in  the  mines  of  this 
country  and  are  rapidly  being  extended,  especially  the  use 
of  waste.  The  filling  of  underground  excavations,  as  stopes, 
with  ore  is  a  method  employed  for  reasons  of  utility  and 
economy  as  well  as  support.  Ore  may  be  located  and 
broken  in  the  stopes  but  not  drawn  off,  except  as  is  found 
necessary  to  provide  room  for  the  operation  of  stoping.  As 
there  is  an  increase  in  volume  of  from  30  to  40  per  cent  in 
broken  ore,  it  is  evident  that  a  certain  amount  must  be 
drawn  off  after  each  round  of  shots  to  give  space  for  sub- 
sequent work  at  the  face.  A  large  amount  of  ore  may  then 
remain  in  the  mine,  forming  an  'ore  reserve.'  The  advan- 
tages of  such  a  system  are:  a  large  force  of  men  may  be 
employed  in  breaking  ore;  less  danger  from  falls  of  rock 
owing  to  rapidity  of  working;  reduced  cost  of  breaking  and 
handling  ore;  a  more  uniform  output;  and  a  more  careful 
grading  of  ores  resulting  from  not  having  to  rush  work  in 
order  to  keep  up  with  the  required  output. 

The  work  at  the  face  is  materially  facilitated  by  this 
method  of  procedure,  as  the  ore  serves  as  a  platform  upon 


l8  ORE  MINING  METHODS 

which  the  drills  are  mounted,  the  height  of  which  may  be 
varied  at  will.  The  ore  while  stored  in  the  s topes  also  serves 
as  a  support  for  the  workings,  reducing  or  eliminating  the 
support  that  would  otherwise  be  necessary.  It  is  difficult  to 
imagine  a  case  where  ore  would  be  introduced  into  a  mine 
or  transferred  to  any  part  of  it  for  support,  owing  to  the 
extra  cost  involved,  as  well  as  the  loss  in  fine  ore  resulting 
from  attrition  in  handling.  That  ore  is  occasionally  so  used 
is  due  either  to  the  fact  that  when  so  employed  its  grade  is 
not  considered  sufficient  at  the  time  to  warrant  treatment,  or 
the  temporary  need  of  support  is  so  urgent  that  it  is  expedi- 
ent to  resort  to  the  use  of  even  a  fair  grade  of  ore. 

The  use  of  waste  in  the  support  of  underground  workings 
is  now  a  well-established  method,  and  its  widespread  appli- 
cation indicates  how  favorably  it  is  looked  upon  by  mining 
men.  The  employment  of  waste-filling  depends  to  a  large 
extent  upon  its  source.  There  are  three  possible  sources  of 
waste,  namely :  that  resulting  from  mining  operations,  being 
sorted  from  the  ore  or  portions  of  the  walls  that  have  to  be 
broken  down  in  cutting  out  the  ore;  that  obtained  from 
special  excavations  made  in  the  vein  walls,  usually  the  hang- 
ing-wall; and  material  from  quarries  or  open-cuts  on  the 
surface  and  the  waste  products  from  concentrating  works, 
such  as  tailings.  The  first  source  mentioned  is  the  most 
important,  as  comparatively  little  labor  is  required  in  placing 
it  properly  in  the  excavation  to  be  supported.  This  is 
particularly  true  in  the  case  of  veins  where  but  a  small  part 
of  the  ore  is  valuable,  the  bulk  of  the  vein-content  being 
used  as  filling;  also  in  certain  cases  where  more  waste  is 


SUPPORT  OF  WORKINGS  19 

required  than  can  be  obtained  from  sorting  the  ore,  the 
additional  amount  being  secured  by  blasting  several  feet 
off  the  walls.  Much  filling  is  now  taken  from  the  surface 
and  by  the  use  of  waste  chutes  is  conducted  to  any  portion 
of  the  mine  desired,  being  distributed  by  cars.  Under- 
ground excavations  opened  especially  to  secure  waste  for 
filling  are  occasionally  made,  but  it  is  a  method  of  procedure 
which  is  liable  to  lead  to  disastrous  results,  as  in  starting 
caves,  unless  the  ground  is  particularly  strong. 

Support  by  Indirect  Means.  —  Indirect  methods  are  re- 
sorted to  wherever  intelligent  supervision  is  given  to  the 
work  and  where  conditions  are  favorable.  The  natural  arch 
formed  by  caving  ground,  or  the  so-called  'dome  of  equi- 
librium,' may  be  employed  to  advantage  in  the  temporary 
support  of  underground  excavations.  By  arching  the  roof 
it  is  often  possible  to  maintain  it  without  any  support  or 
with  very  temporary  constructions.  The  character  of  the 
ground  is  the  governing  factor  in  this  work,  certain  forma- 
tions not  being  sufficiently  strong  to  stand  even  with  short 
spans  and  high  arches,  while  other  specially  strong  forma- 
tions may  be  given  exceedingly  long  spans  and  low  arches. 
The  wide  stopes  of  the  Homestake  and  Alaska-Treadwell 
mines  illustrate  remarkably  well  the  application  of  the 
'dome  of  equilibrium7  to  strong  and  stable  formations. 

Caving  may  be  employed  as  a  supplementary  method 
following  some  well-defined  system,  usually  with  timber 
supports,  until  its  limit  of  applicability  has  been  reached  or 
exceeded.  The  weight  of  the  unmined  ore  together  with  the 
mass  of  broken  waste  and  timber  lying  above  the  ore  is 


20  ORE  MINING   METHODS 

temporarily  supported  by  pillars  of  ore  and  timber.  In  the 
course  of  time  the  pillars  begin  to  break  up,  and  by  care- 
fully and  systematically  removing  the  timber  supports  and 
attacking  the  pillars  in  such  a  manner  as  to  assist  the  dis- 
integration, practically  all  of  the  ore  remaining  above  the 
level  worked  may  be  drawn  off  with  little  or  no  danger  to  the 
laborers  or  the  integrity  of  mine  workings. 

The  support  of  the  caving  ore  and  overlying  caved 
material  is  of  the  most  temporary  character  and  really 
amounts  to  a  well-defined  and  scientific  control  of  the 
movement  of  the  caving  mass  rather  than  its  definite 
support. 

In  order  that  the  methods  of  support  discussed  above  may 
be  rendered  still  more  comprehensive  the  following  brief 
statements  are  made  regarding  their  application  and  com- 
parative advantages  and  disadvantages. 

Pillars  of  mineral  constitute  the  most  natural  form  of 
support  for  underground  workings.  The  advantages  in  their 
use  are :  the  vein-content  left  in  place  is  probably  the  strong- 
est possible  support  obtainable;  support  can  be  provided 
at  any  desired  point;  there  is  no  expense  attendant  upon 
their  use  and  no  risk  from  fire.  The  disadvantages  are :  loss 
of  mineral  when  formed  in  ore;  a  tendency  to  make  them  too 
small  to  save  ore;  also  a  like  tendency  and  for  similar  reasons 
to  place  them  irregularly  or  dispense  with  them  altogether. 

Props  or  Posts  can  be  used  to  advantage  in  a  vertical  or 
nearly  vertical  position  only.  Their  chief  advantage  lies  in 
the  ease  with  which  they  can  be  placed  and  removed  if 
desired. 


SUPPORT   OF  WORKINGS  21 

Stulls  have  a  very  much  wider  range  of  application  than 
posts,  as  they  can  be  employed  in  veins  ranging  from  an 
inclination  of  about  10°  to  the  vertical.  When  properly 
placed  they  are  not  affected  by  slight  movements  of  the  walls 
and  are  therefore  suitable  for  a  great  variety  of  conditions. 
They  may  be  employed  as  supports  of  scaffoldings  upon 
which  drills  are  mounted,  forming  '  stull-levels '  and  '  waste- 
stulls.' 

Cribs  or  Bulkheads  owing  to  their  width  are  more  stable 
than  posts  or  stulls,  but  to  give  the  best  results  must  be 
built  practically  vertical.  They  cannot  be  used  to  advan- 
tage except  in  horizontal  or  slightly  inclined  deposits  or  wide 
veins.  While  readily  built  they  are  difficult  to  take  down, 
especially  when  filled  with  waste,  and  occupying  considerable 
space  encumber  the  workings,  interfering  with  handling  ore 
and  supplies. 

Square-Sets  like  cribs  must  be  built  along  horizontal 
and  vertical  lines  and  are  therefore  confined  to  compara- 
tively wide  veins  and  massive  deposits.  They  are  expensive 
to  frame  and  place  and  unless  filled  with  waste  soon  buckle 
and  crush,  both  under  their  own  weight  and  that  of  the  walls. 
However,  for  the  support  of  large  openings  they  have  proved 
indispensable  in  the  past,  the  ease  with  which  extensions  can 
be  made  in  any  direction  being  a  most  important  factor  in 
mining. 

Filling  mine  workings,  especially  with  waste,  is  growing 
in  favor  owing  to  the  facts  that  support  can  be  placed 
quickly  and  readily;  the  waste  of  the  mine  can  be  disposed 
of  at  minimum  expense,  and  cheap  material  can  be  trans- 


22  ORE   MINING   METHODS 

f erred  underground  with  little  work;  it  can  be  used  a  num- 
ber of  times,  being  drawn  from  one  part  of  the  mine  to 
another;  a  good  support  uniformly  distributed  over  the  walls 
is  obtained,  and  there  is  no  fire  risk. 

The  disadvantages  resulting  from  the  use  of  filling  are 
shrinkage  of  filling  disturbing  workings  and  a  tendency  for 
the  filling  to  become  quick  and  flow  under  pressure. 

Caving  as  an  indirect  method  of  support  is  applicable  to 
large  deposits  only;  requires  continuous  and  rapid  work; 
the  loss  of  mineral  may  be  considerable  owing  to  the  move- 
ment of  the  caving  mass  getting  beyond  control;  and  a  large 
amount  of  timber  is  required  with  certain  deposits.  The 
advantages  are:  a  large  output  at  moderate  cost;  operations 
must  begin  near  the  surface;  and  the  overlying  rock  must 
cave  readily. 


CHAPTER  II 

METHODS  OF  STOPING  AND  HANDLING  ORE 
IN  STOPES 

METHODS  OF  STOPING 

THE  openings  in  metal  mines  from  which  ore  is  taken  are 
called  stopes  and  the  methods  employed  in  breaking  down 
the  ore  are  known  as  stoping.  Stoping  then  constitutes 
the  fundamental  operation  in  the  extraction  of  ore  and  must 
be  well  understood  before  a  discussion  of  methods  of  mining 
is  undertaken.  Under  certain  conditions  the  methods  of 
stoping  constitute  in  themselves  methods  of  mining  and 
give  the  latter  the  name  of  the  kind  of  stoping  employed. 

The  methods  of  stoping  employed  in  the  mines  of  the 
United  States  and,  in  fact,  throughout  the  mining  world  may 
be  outlined  as  follows: 

i.  Overhand  Stoping. 

.2.  Underhand  Stoping. 

3.  Breast  Stoping. 

4.  Resuing. 

Other  methods  of  stoping  may  result  through  combining 
overhand  and  underhand  stoping,  such  as: 

1.  Combined  or  overhand-underhand  stoping. 

2.  Side  stoping,  sometimes  called  breast  stoping. 

3.  Longwall  stoping  or  cutting-out  stoping. 

23 


24  ORE  MINING  METHODS 

The  direction  of  the  working  face  with  respect  to  the 
lines  of  development,  as  levels,  raises  and  winzes,  furnishes 
the  basis  for  the  above  classification.  The  methods  of 
stoping  as  outlined  may  then  be  defined  as  follows:  Over- 
hand stoping  is  working  up  the  dip  and  usually  in  a  direc- 
tion diagonal  to  raises  and  winzes;  underhand  stoping  is 
working  down  the  dip  also  in  a  direction  diagonal  to  raises 
and  winzes;  breast  stoping  may  be  either  overhand  or  under- 
hand stoping  applied  to  deposits  of  slight  inclination  and 
resembles  breast  work  in  coal  mining;  combined  stoping  is 
where  both  overhand  and  underhand  stoping  are  carried  on 
in  the  same  working  place  or  stope,  the  two  lines  of  working 
faces  extending  diagonally  up  and  down  the  stope  from  a 
common  point  in  the  center  of  the  stope;  side  stoping  is 
where  the  working  face  is  parallel  with  the  winzes;  while 
longwall  stoping  has  the  working  face  parallel  with  the 
levels.  These  terms  are,  however,  more  or  less  elastic  and 
may  be  employed  differently  in  various  districts  and  mines. 

The  conditions  influencing  and  controlling  the  choice  of 
method  of  stoping  are  as  follows: 

1.  Character  of  ore  and  its  value. 

2.  Occurrence  of  valuable  mineral. 

3.  Width  of  vein  or  deposit. 

4.  Dip  and  pitch  of  ore  body. 

5.  Size  and  shape  of  ore  bodies  other  than  in  veins. 

6.  Character  and  condition  of  wall-rocks. 

7.  Cost  of  timber  for  support. 

Of  the  conditions  given  above  that  of  dip  or  inclination 
probably  exerts  the  greatest  influence  on  method  of  stoping, 


STOPING   AND   HANDLING   ORE  IN   STOPES  25 

being  the  principal  factor  in  the  choice  between  overhand 
and  underhand  methods.  Wide  veins  or  large  deposits 
while  often  worked  by  overhand  stoping  may  necessitate 
breast  stoping  wholly  or  in  part.  The  character  and 
occurrence  of  the  valuable  mineral  while  not  necessarily 
influencing  the  method  of  attack  may  require  modifications 
which  are  more  or  less  radical.  The  character  of  wall-rock 
concerns  the  method  of  support  mainly  and  therefore  affects 
the  general  scheme  of  working  rather  than  the  method  of 
attack  or  method  of  stoping. 

The  handling  of  mineral  in  stopes  varies  widely  with  the 
method  of  stoping  employed,  and  may  even  necessitate  a 
change  in  method  in  order  that  the  work  may  be  facilitated 
and  cheapened.  The  factors  which  influence  the  handling  of 
mineral  in  stopes  are,  in  order  of  importance,  dip  and  width 
of  vein  and  character  and  occurrence  of  mineral. 

Overhand  Stoping.  —  This  method  of  stoping  is  probably 
more  extensively  employed  than  the  other  methods,  being 
used  in  practically  all  kinds  of  metal  mines  where  condi- 
tions are  at  all  suitable.  Overhand  stoping  is  commonly 
employed  in  both  narrow  and  wide  veins,  in  moderately 
highly  or  highly  inclined  stratified  deposits,  and  in  massive 
deposits. 

The  location  of  a  body  of  ore  having  been  determined 
by  levels  and  raises  or  winzes  driven  through  it,  the  work 
of  cutting  out  the  ore  is  begun  by  attacking  it  on  one  or 
both  sides  of  a  raise  or  winze,  which  connects  the  two  levels 
and  extends  through  the  ore  located  at  that  point.  (See 
Figs.  5  and  6.) 


26 


ORE  MINING  METHODS 


As  there  are  several  methods  of  procedure  that  are  de- 
pendent upon  the  character  and  occurrence  of  the  mineral 
in  the  vein,  the  determining  conditions  should  now  be  stated. 
Where  all  of  the  vein  matter  is  sufficiently  valuable  to  mine 


FIG.  5. —  Overhand  Sloping,  'Breaking-Through.' 

it  may  be  broken  down,  transferred  to  the  level  below,  loaded 
into  cars  and  hauled  away.  There  are  cases,  however, 
where  it  is  not  possible  or  advisable  to  dispose  of  the  ore  as 
rapidly  as  it  is  mined,  although  its  preparation  for  with- 
drawal from  the  stopes  is  an  important  consideration.  As 
ore  when  broken  increases  in  bulk  about  40  per  cent  it  is 
evident  that  to  provide  working  space  for  the  miners  at  the 


STOPING  AND  HANDLING  ORE  IN  STOPES  27 

face  a  certain  amount  of  the  broken  ore  will  have  to  be  drawn 
off  after  a  certain  advance  has  been  made.  This  is  known 
as  '  shrinkage '  stoping,  while  the  ore  remaining  in  the  stope 
is  called  an  'ore  reserve'  and  serves  a  useful  purpose  in 
regulating  the  output  of  the  mine.  On  the  other  hand  the 
bulk  of  the  vein  matter  may  be  barren  or  so  low-grade  as 
to  warrant  only  the  least  possible  handling,  in  which  case 
provision  must  be  made  for  both  the  storage  of  the  waste 
and  the  disposal  of  the  valuable  mineral. 

In  either  of  the  cases  mentioned  some  provision  must  be 
made  for  the  support  of  the  ore  or  waste  left  in  the  stopes,  if 
that  is  done.  If  all  of  the  ore  is  removed  from  the  stopes  as 
rapidly  as  it  is  broken  down,  then  supports  for  the  main- 
tenance of  walls  and  protection  of  levels  is  all  that  is  neces- 
sary. Stope  marked  A-i,  in  Fig.  6,  illustrates  the  first 
case  mentioned,  where  the  ore  is  drawn  off  as  soon  as  broken 
down.  Stopes  B  and  B-i  may  be  taken  as  representing 
the  condition  where  ore  is  stored  in  the  stopes,  forming  an 
ore  reserve.  Stope  A  may  represent  the  condition  existing 
in  a  precious-metal  mine  where  the  gold  or  silver  occurs  in 
small  veins  or  stringers,  the  bulk  of  the  vein-filling  being 
barren  or  low-grade  and  is  left  in  the  stope. 

Stopes  may  be  opened  in  two  ways,  namely,  by  beginning 
at  a  winze  or  raise,  or  by  first  driving  a  'raise  stope.'  Raise 
stoping  differs  from  driving  raises  mainly  in  width  of  passage 
or  cut  made,  the  usual  width  for  a  raise  stope  varying  from 
20  to  25  feet.  From  such  a  starting  point  the  height  of  the 
drift  may  be  increased  by  a  'cutting-out'  stope,  and  con- 
sists in  removing  the  vein-content  in  a  more  or  less  regular 


28 


ORE  MINING  METHODS 


O 

be 

G 

I 


STOPING  AND   HANDLING   ORE  IN   STOPES  29 

way,  i.e.,  by  cutting  out  a  portion  of  definite  width  from  the 
back  of  the  drift.  This  is  the  usual  method  of  procedure 
when  a  stope  is  started  after  the  level  has  been  run.  When, 
however,  drifting  precedes  breaking  ore  or  stoping  by  but 
a  few  feet,  'drift  stoping'  is  employed  in  enlarging  the  drift 
or  level  previous  to  the  actual  work  of  stoping,  or  cutting- 
out  stoping.  Drifting  and  stoping  are  then  combined  in  one 
operation  and  consist  in  carrying  a  face  about  25  feet  high 
practically  the  full  width  of  the  vein. 

As  each  cutting-out  stope  is  advanced,  receding  from  the 
common  starting  point,  and  is  followed  by  others  at  regular 
intervals,  the  working  face  of  the  stope  assumes  an  inverted- 
stepped  appearance  as  shown  in  stopes  B  and  B-i,  Fig.  6. 
The  successive  stope  faces  are  then  called  'back-stopes,' 
being  numbered  in  order  from  the  drift-stope  upward 
(B,  Fig.  6).  The  parts  of  the  stope  designated  as  'toe'  and 
'heel'  are  shown  in  B-i. 

The  usual  practice  in  the  mines  of  the  United  States  is  to 
carry  the  stopes  up  from  the  levels  without  leaving  a  row 
of  pillars  directly  above  them  as  shown  in  stope  B-i.  Wall 
pillars  are,  however,  commonly  left  for  support  (see  stope 
A-i),  which  is  the  usual  practice  in  veins  of  moderate 
inclinations.  In  more  highly  inclined  veins,  unless  of  too 
great  width,  stulls  and  lagging  with  ore  or  waste-filling  are 
employed.  (See  stopes  A  and  B.) 

Overhand  stoping  is  employed  in  veins  varying  in  dip 
from  a  few  degrees  up  to  the  vertical,  but  may  be  used  more 
readily  in  veins  of  slighter  inclination  than  underhand 
stoping. 


ORE   MINING   METHODS 


FIG.  7. —  An  i8-inch  Stope  in  the  Rand  Mines,  South  Africa. 

Underhand  Sloping.  —  In  many  respects  underhand  re- 
sembles overhand  sloping,  and  may  be  said  to  be  overhand 
sloping  upside  down,  i.e.,  the  work  of  breaking  the  ore  is 
downward  instead  of  upward.  (See  slopes  C  and  B,  Fig.  6.) 
The  relation  between  the  sloping  face  and  the  lines  of  devel- 
opment is  also  similar  to  that  in  overhand  work. 

The  Cornish  system  of  underhand  sloping  consists  in 
sinking  a  pit  in  the  floor  of  a  level  and  then  beginning  the 
work  of  removing  the  ore  by  working  laterally  therefrom. 


STOPING  AND   HANDLING   ORE   IN   STOPES  31 

This  method  has  two  serious  disadvantages,  namely:  all 
the  ore  has  to  be  shoveled  out  or  raised  by  windlass,  and  the 
accumulation  of  water  in  the  pit  so  formed  will,  if  the  mine 
is  wet,  necessitate  pumping.  Where  a  piece  of  ground  of 
limited  extent  is  known  to  contain  valuable  ore  the  Cornish 
system  of  stoping  may  be  not  only  advisable  but  necessary. 
When,  however,  ore  has  been  blocked  out  between  levels 
and  known  to  extend  for  some  distance  along  the  stope,  the 
method  employed  in  removing  the  ore  should  be  undertaken 
on  a  larger  scale  and  more  systematically.  Provision  will 
have  to  be  made  also  for  handling  the  ore  quickly  and  cheaply 
and  for  keeping  the  workings  free  from  water.  This  can 
readily  be  accomplished  by  beginning  stoping  on  the  sides 
of  a  raise  or  winze  connecting  levels.  Ore  and  water  are 
both  discharged  through  the  connecting  passage  to  the  lower 
level,  the  former  being  loaded  into  cars  while  the  latter  is 
conducted  by  drains  to  the  sumps  located  in  the  levels  or 
at  the  foot  of  the  shaft.  (See  left-hand  portion  of  stope  C.) 

Underhand  stoping  unlike  overhand  work  is  not  applicable 
to  deposits  where  only  a  small  portion  of  the  vein-content  is 
valuable,  for  the  very  evident  reason  that  there  is  no  con- 
venient place  to  store  the  waste.  Occasionally  a  line  of 
stulls  may  be  set  in  the  stope,  with  a  flooring  of  lagging, 
thus  forming  a  staging  upon  which  a  limited  quantity  of 
waste  may  be  thrown.  The  method  is,  however,  applicable 
to  both  high-  and  low-grade  deposits  the  whole  or  a  large 
part  of  which  is  workable,  also  to  massive  deposits  where 
the  work  of  stoping  is  carried  on  in  horizontal  floors. 

Underhand  stoping  may  be  employed  on  quite  a  range  of 


32  ORE  MINING  METHODS 

dips,  but  is  most  successful  in  veins  of  50°  and  up,  due  to  the 
necessity  of  handling  ore  by  gravity. 

Underhand  stoping  may  be  done  in  very  small  veins  even 
as  narrow  as  18  inches.  (See  Fig.  7.) 

Both  overhand  and  underhand  stoping  may  begin  next  to 
the  shaft,  the  width  of  shaft  pillars,  if  employed,  determining 
the  beginning  of  the  stopes.  A  winze '  or  raise  is  driven 
connecting  the  levels,  forming  the  shaft  pillars  and  at  the 
same  time  providing  a  point  of  attack  in  stoping.  In  over- 
hand work  the  stope  is  begun  on  the  corner  where  the  winze 
and  level  intersect,  successive  cuts  increasing  both  the  width 
and  height  of  the  stope.  With  underhand  stoping,  unless 
no  arch  pillars  are  left,  the  work  of  removing  the  ore  can- 
not begin  until  a  drift  is  run  below  the  arch  pillars,  thus 
definitely  determining  their  position  and  forming  them.  At 
the  intersection  of  the  drift  and  winze  or  raise  the  work  of 
stoping  may  begin  and  extend  downward  until  the  level 
below  is  reached.  The  beginning  of  stoping  next  to  the 
shaft  is  shown  in  stopes  B  and  B-i  for  overhand  stoping 
and  in  stopes  C  and  C-i  for  underhand  work. 

Underhand  stoping  is  largely  employed  in  massive  de- 
posits and  in  slightly  inclined  bedded  deposits  of  consider- 
able thickness.  The  opening  of  a  stope  may  be  accom- 
plished in  one  of  two  ways,  namely :  a  shaft  may  be  sunk  to 
or  near  the  deposit  and  a  drift  run  into  the  ore  body  at  a 
point  as  near  the  top  as  possible;  or  an  ore  body  having  been 
entered  by  an  exploratory  drift,  any  height  of  stope  may  be 
developed  by  running  a  raise  to  the  top  of  the  deposit.  In 
the  first  case  the  stope  may  be  increased  in  height  by  cutting 


STOPING  AND  HANDLING  ORE  IN  STOPES 


33 


3 

'3* 
o 

C/2 

"S 

CM 


a 

<u 

Q 


o 

IM 
O 
tn 

I 


34  ORE  MINING  METHODS 

out  the  floor  of  the  drift,  work  beginning  at  the  shaft  and 
extending  to  the  ore  body  where  benches  are  formed  by 
successively  lifting  the  floor  of  the  drift.  The  usual  height 
of  the  individual  benches  is  8  to  10  feet,  but  a  number  may 
be  run  together  forming  a  single  bench  of  50  to  60  feet  in 
height.  The  raise  in  the  second  case  forms  the  initial  point 
of  attack  and  takes  the  place  of  the  shaft,  the  subsequent 
operations  being  identical  with  those  described  above. 
(See  Fig.  8.) 

A  plan  of  a  mine  workings  in  which  underhand  stoping 
has  been  employed  is  shown  in  Fig.  9,  the  shaded  portions 
indicating  parts  of  the  floor  that  have  been  stoped  to  a 
lower  level  than  the  workings  in  main  body  of  the  deposit. 

As  the  shape  and  slope  of  the  face  of  the  stope  in  such 
deposits  are  entirely  under  the  control  of  the  miner  and  not 
dependent  upon  the  dip  of  a  vein,  the  passing  of  the  ore  to 
the  foot  of  the  stope  can  be  readily  accomplished,  its  trans- 
ference to  the  shaft  being  done  in  cars. 

Combined  Stoping.  —  Occasionally  a  stope  will  be  worked 
by  both  overhand  and  underhand  stoping,  overhand  being 
employed  at  the  bottom  and  underhand  at  the  top  of 
the  stope.  The  dip  of  the  vein  determines  the  propor- 
tionate length  of  the  two  working  faces;  with  certain  dips 
as  50  to  55°  the  length  of  the  underhand  stoping  face  exceeds 
that  of  the  overhand  face,  while  with  dips  of  25  to  30°  the 
reverse  is  true.  The  reason  why  underhand  stoping  is 
employed  at  the  top  and  overhand  at  the  bottom  of  the 
stope  is  that  with  a  reversal  of  the  arrangement  a  reentrant 
angle  would  be  formed  between  the  two  working  faces,  thus 


STOPING  AND  HANDLING   ORE  IN   STOPES 


35 


hfl 

C 

'Su 
o 

in 
"S 


36  ORE  MINING  METHODS 

forming  a  'tight  corner'  which  is  difficult  to  work.  An 
advantage  of  the  usual  arrangement  is  that  the  angle  formed 
by  the  faces,  coming  as  it  does  in  the  center  of  the  stope, 
makes  the  forming  of  wall  pillars  comparatively  easy;  the 
more  acute  the  angle  the  more  readily  are  the  pillars 
formed. 

With  high  dips  the  underhand  face  increasing  in  length 
has  all  the  advantages  of  underhand  stoping  and  at  the 
same  time  materially  assists  in  handling  waste  and  placing 
it  on  '  stull  floors '  in  the  overhand  part  of  the  stope.  When 
the  dip  is  such  as  to  require  that  the  overhand  face  be  longer, 
the  short  underhand  stope  above  may  be  of  advantage  in 
handling  a  considerable  part  of  the  ore  at  the  top  of  the 
stope,  which  can  be  thrown  or  raised  to  the  level  above 
instead  of  being  transferred  down  through  the  stope  to  the 
level  below.  Higher  stopes  can  be  worked  to  advantage 
by  combining  overhand  and  underhand  stoping,  which  per- 
mits the  levels  to  be  placed  farther  apart  and  so  reducing 
the  cost  of  development  work.  The  chief  advantage  of  the 
method  then  lies  in  the  convenience  of  handling  ore  and  waste 
in  the  stope. 

Breast  Stoping.  —  When  the  inclination  of  the  vein  or 
bed  is  such  that  the  broken  ore  cannot  be  passed  to  the 
level  below  by  gravity,  but  remains  close  to  the  face  and  must 
be  loaded  into  cars  at  that  point,  neither  overhand  nor 
underhand  stoping  can  be  employed  to  advantage.  The 
method  employed  is  then  ordinary  breast  work,  and  the  di- 
rection of  the  face  may  be  carried  in  practically  any  direction. 
This  method  permits  the  placing  of  holes  so  as  best  to 


STOPING  AND   HANDLING   ORE  IN   STOPES  37 

take  advantage  of  the  conditions  existing  at  the  face;  the 
principal  disadvantage  being  that  the  cars  must  be  run  to 
the  face,  thus  increasing  the  cost  of  handling. 

Side  Stoping.  —  As  previously  pointed  out,  side  stoping  and 
breast  stoping  are  often  spoken  of  as  being  similar  opera- 
tions, but  strictly  speaking  they  are  not.  Side  stoping  is 
carried  on  parallel  with  winzes  or  raises,  which  as  in  the 
case  of  the  other  methods  of  stoping  is  the  initial  point 
of  attack.  This  method  of  stoping  is  not  confined  to 
slight  inclinations  as  would  be  the  case  were  it  similar  to 
breast  stoping. 

There  is  no  method  of  stoping  in  which  the  direction  of 
the  working  face,  the  distinguishing  characteristic  of  the 
methods,  is  more  than  approximately  maintained,  and  there 
is  no  method  of  stoping  which  is  apt  to  have  the  direction  of 
the  face  vary  more  than  side  stoping.  Raise  stoping  and 
side  stoping  are  similar  if  parallelism  to  raises  and  winzes 
is  the  distinction,  but  raise  as  well  as  drift  and  cutting-out 
stoping  are  phases  of  overhand  stoping;  however,  as  the 
term  side  stoping  has  been  applied  to  a  certain  direction  of 
working  in  stoping,  and  as  it  is  similar  to  raise  stoping,  the 
name  may  be  applied  to  both  alike.  (See  stope  A,  left- 
hand  side,  Fig.  6.)  The  first  cut  in  side  stoping  is  driven 
directly  up,  the  dip  being  commonly  employed  in  forming 
shaft  pillars,  dead-ends,  etc.,  and  in  starting  cutting-out 
stopes  in  overhand  work.  When  employed  in  this  manner 
side  stoping  serves  as  a  supplementary  method  to  overhand 
stoping,  but  its  application  may  be  extended  to  the  regular 
work  of  breaking  ore,  successive  cuts  being  taken  off  the 


38  ORE  MINING  METHODS 

sides  of  the  first  side  stope  run.  The  tendency  is,  however, 
for  the  direction  of  the  work  to  change  so  radically  as  to 
lose  its  identity  as  side  stoping  and  merge  into  overhand 
work  or  underhand  work,  usually  the  former. 

Longwall  Stoping.  —  Raise  stoping  has  been  shown  to  be 
a  phase  of  overhand  stoping.  In  a  similar  manner  cutting- 
out  stoping  corresponds  to  longwall  work.  Further,  breast 
and  side  stoping  may  be  said  to  be  similar  to  longwall  work 
unless  parallelism  with  the  longer  dimension  of  the  stope  is 
a  desideratum. 

As  usually  carried  on,  longwall  stoping  is  applied  to  that 
class  of  overhand  work  where  the  working  face  is  parallel 
with  the  levels  and  constitutes  an  important  part  of  the 
work  of  breaking  ore  as  the  work  of  stoping  is  carried  on  in 
many  districts.  (See  stope  A,  Fig.  6.)  While  longwall 
stoping  may  be  employed  in  veins  of  slight  or  moderate 
inclination,  as  when  breast  stoping  is  applicable,  and  cars 
are  run  parallel  with  the  face,  yet  it  is  just  as  often  employed 
in  steeply  inclined  veins  where  ore  or  waste  is  stored  in  the 
stopes.  (See  stope  A,  Fig.  6.)  Although  there  may  be 
no  advantage  in  breaking  ore  by  this  method,  yet  there  is  a 
positive  advantage  in  handling  ore  on  a  level  floor,  compared 
with  similar  work  on  an  irregular  and  sloping  bank  of  ore 
as  in  overhand  stoping.  (Compare  stopes  A  with  B  and 
B-i,  Fig.  6.) 

Resuing.  —  This  method  is  a  special  application  of  stop- 
ing to  narrow  veins  or  stringers  and  is  in  reality  a  stripping 
method.  Resuing  consists  in  opening  up  the  stopes  not  in 
the  vein  but  in  the  wall-rock,  by  whatever  method  of  stoping 


STOPING  AND   HANDLING   ORE   IN   STOPES  39 

seems  best  adapted  to  the  existing  conditions,  and  when 
sufficient  space  has  been  provided  by  stripping  one  wall 
from  the  ore  it  is  broken  down  and  handled  practically 
independently  of  the  waste. 

When  the  values  are  definitely  known  to  occur  in  the  vein 
alone,  this  method  of  procedure  is  especially  applicable,  but 
when,  as  often  happens,  the  values  also  extend  into  the  walls 
the  usual  methods  of  stoping  are  probably  more  applicable. 
The  extra  width  of  drifts  and  stopes  may  also  serve  to  un- 
cover and  discover  other  workable  portions.  Where  the 
condition  of  the  vein-filling  and  wall-rock  permit,  much 
cleaner  ore  can  be  produced,  which  may  be  the  determining 
factor  in  the  economical  working  of  a  given  deposit.  How- 
ever, the  sorting  of  waste  rock  under  the  unfavorable  con- 
ditions existing  underground,  often  resulting  in  the  necessity 
of  sending  considerable  waste  rock  to  the  surface  and  the 
treatment  of  the  same,  may  make  it  inadvisable  to  employ 
resuing.  For  narrow  vein  work  see  Fig.  7. 

Resume  of  Stoping.  —  The  conditions  under  which  the 
different  methods  of  stoping  are  especially  applicable,  with 
the  advantages  and  disadvantages  of  their  use,  are  as 
follows: 

Overhand  Stoping  has  a  wide  range  of  application  both 
as  to  character,  inclination  and  width  of  deposit.  The 
method  is  employed  in  very  narrow  and  very  wide  veins 
and  even  massive  deposits,  but  when  considered  as  a  distinct 
method  of  mining  its  application  is  limited  to  moderately 
narrow  veins  or  beds,  as  from  4  to  1 2  feet,  and  to  inclinations 
of  i o  to  90°  with  the  horizontal. 


40  ORE  MINING  METHODS 

The  advantages  of  overhand  stoping  are: 

1.  Levels  may  be  driven  at  considerable  distance  apart, 
ranging  from   100  to   150  feet,  and  occasionally  greater 
distanced. 

2.  Greater  safety  to  men,  as  the  roof  is  accessible  and  can 
be  examined  and  made  safe  as  signs  of  weakness  develop. 
This  is  especially  true  when  the  roof  is  the  working  face, 
as  is  the  case  with  steeply  inclined  deposits. 

3.  A  large  working  force  can  be  employed  in  a  compara- 
tively small  space,  which  results  in  reduced  cost  of  extraction 
per  ton  of  ore. 

4.  Both  ore  and  waste  can  be  stored  in  the  stopes,  which 
assists  materially  in  the  support  of  the  workings. 

5.  The  ore  as  broken  down  falls  free  of  the  face  and  by 
gravity  moves  toward  the  point  of  delivery. 

6.  Where  ore  is  stored  in  the  stopes  a  ' reserve'  is  formed, 
thus  regulating  and  maintaining  the  output  independently 
of  temporary  stoppage  of  mining  operations. 

7.  Large  and  regular  outputs  are  possible. 

8.  The  face  of  the  stope  is  usually  opposite  a  number  of 
chutes  into  which  the  ore  may  be  thrown. 

The  disadvantages  of  overhand  stoping  are: 

1.  Considerable  timber  is  required  for  support,  or  if  wall 
pillars  are  employed  a  loss  of  ore  may  result. 

2.  When  ore  is  left  in  the  stopes  it  serves  as  a  platform 
for  the  men  to  work  upon,  which  may  prevent  a  stope  being 
emptied  until  all  ore  is  removed  up  to  the  arch  pillars.     This 
difficulty  may  be  largely  obviated  by  using  'stull  floors,7 
but  this  necessitates  the  use  of  considerable  more  timber. 


STOPING  AND  HANDLING   ORE  IN   STOPES  41 

3.  Dust  is  troublesome,  especially  in  dry  mines,  as  the 
holes  are  largely  drilled  'dry.'  By  a  slightly  different 
arrangement  of  the  working  face  the  direction  of  the  holes 
may,  however,  be  altered,  changing  them  from  'dry'  to 
'wet.' 

Underhand  Sloping  is  also  employed  in  both  veins  and 
massive  deposits,  but  is  applicable  to  higher  inclinations 
(38  to  90°)  in  veins  than  is  overhand  work.  As  a  distinct 
method  of  mining,  and  not  simply  as  a  method  of  attacking^ 
the  face,  underhand  stoping  is  applied  equally  well  to  narrow 
and  moderately  wide  veins  and  massive  deposits. 

The  advantages  of  underhand  stoping  are: 

1.  Ease  in  drilling  and  blasting,  especially  when  hand 
drilling  is  done. 

2.  Comparatively  small  amount  of  timber  is  used. 

3.  When  proper  slopes  are  maintained  in  the  stopes  the 
ore  can  be  handled  largely  by  gravity. 

4.  Little  trouble  is  experienced  with  dust. 
The  disadvantages  of  underhand  stoping  are: 

1.  The  method  is  limited  to  veins  or  highly  inclined 
bedded  deposits  where  all  or  a  large  part  of  the  deposit  is 
of  sufficient  value  to  mine. 

2.  Levels  are  run  closer  together  in  order  to  reduce  the 
amount  of  exposed  roof  and  consequently  diminish  the  dan- 
ger of  falls. 

3.  The  working  face  is  small,  the  lower  part  of  the  stope 
face  being  largely  covered  with  broken  ore;  the  output  is 
therefore  small. 

4.  Inconvenience  resulting  from  having  no  'ore  reserve,' 


42  ORE  MINING  METHODS 

often  necessitating  underground  or  surface  ore  bins  of  suffi- 
cient capacity  to  maintain  the  output  of  the  mine  should  it 
be  necessary  to  temporarily  stop  breaking  ore. 

5.  The  difficulty  experienced  in  disposing  of  waste  sorted 
from  the  ore. 

6.  Loss  of  ore  in  pillars. 

Breast  Sloping  is  applicable  to  inclinations  below  the 
angle  of  repose  of  broken  ore,  which  is  about  38°  with  the 
horizontal.  As  a  rule,  however,  breast  stoping  is  usually 
carried  on  at  much  lower  dips  as  under  10°.  Thick  deposits 
may  be  worked  in  benches,  but  this  usually  leads  to  a  com- 
bination of  breast  and  underhand  work.  A  deposit  10  feet 
thick  can  readily  be  worked  by  breast  stoping;  the  height 
of  face  increasing  the  fall  and  consequently  the  distance  that 
the  ore  will  travel  from  the  face  on  moderate  dips. 

The  advantages  of  breast  stoping  are : 

1.  Deposits  of  low  dip  can  readily  be  worked. 

2.  The  best  conditions  for  mounting  drills  and  taking 
advantage  of  working  face  are  obtained. 

3.  Cars  may  be  run  close  to  the  stope  face. 

4.  Considerable  waste  may  be  left  in  stopes  without 
extra  handling. 

5.  Ease  of  entrance  and  exit  to  and  from  the  stopes. 
The  disadvantages  of  breast  stoping  are: 

1.  Levels  are  close  together. 

2.  Much  timber  is  used  for  support. 

3.  Extra  cost  of  laying  track  and  maintaining  proper 
grade  to  working  face. 

4.  Difficulty  in  handling  ore  in  stopes. 


STOPING   AND   HANDLING   ORE   IN   STOPES  43 

Resuing  is  applicable  to  very  narrow  veins  alone,  i.e., 
under  30  inches  in  width;  its  chief  advantage  being  that  a 
cleaner  grade  of  ore  can  be  mined  than  when  both  vein  and 
walls  are  broken  together;  further,  it  is  often  useful  in  open- 
ing up  unsuspected  bodies  of  ore  existing  in  the  walls,  but  as 
the  work  is  confined  to  one  wall  only  such  application  is 
limited. 

Other  Methods  of  Sloping  such  as  combined,  side  and  long- 
wall  stoping  are  special  applications  of  overhand  and  under- 
hand stoping  and  are  therefore  employed  under  somewhat 
similar  conditions,  especially  as  to  thickness  and  inclination 
of  deposit. 

The  advantages  of  combined  stoping  are: 

1.  Long  stope  backs,  i.e.,  higher  stopes  may  be  employed 
than  with  underhand  stoping  especially. 

2.  Wall  pillars  can  readily  be  formed  at  the  junction  or 
heel  of  the  overhand  portion  of  the  stope. 

3.  Waste  can  be  stowed  to  advantage  on  lagged  stulls  in 
the  overhand  portion  of  the  stope. 

4.  A  certain  amount  of  ore  can  be  transferred  to  the 
level  above  from  the  underhand  portion  of  the  stope,  thus 
reducing  the  amount  that  must  be  handled  below. 

5.  The  intermediate  dips  between  those  to  which  over- 
hand and  underhand  stoping  are  applicable  can  be  worked 
to  advantage  by  this  method. 

The  disadvantages  of  combined  stoping  are: 

i.   The  limitations  as  to  dip  vary  probably  between  35 

and  50°,  above  and  below  which  the  method  merges  into 

all  overhand  or  underhand  work. 


44  ORE  MINING  METHODS 

2.  Tight  corners  are  formed  both  at  the  top  and  bottom 
of  the  stope,  when  lines  of  pillars  are  left  for  the  protection 
of  the  miners  in  the  stopes  and  levels. 

Side  Sloping  is  not  very  extensively  employed,  having 
special  application  in  cutting  out  and  forming  pillars,  such 
as  shaft  pillars  and  dead-ends,  but  is  used  very  little  in  the 
operation  of  breaking  ore.  Its  principal  advantage  lies  in 
the  fact  that  it  is  straight-cut,  up-dip  work,  in  which  drilling 
and  blasting  can  readily  be  done,  the  face  clearing  itself  by 
gravity.  The  tendency  for  the  face  to  narrow,  due  to  the 
tight  corners  and  the  limited  space  in  which  work  must  be 
done,  especially  in  making  the  first  cut,  is  the  chief  objec- 
tion to  the  method. 

Longwall  Sloping  is  strictly  an  overhand  method  and  is 
extensively  employed  in  the  whole  range  of  dips  to  which 
overhand  stoping  can  be  successfully  applied. 

Probably  no  class  of  overhand  stoping  presents  more 
advantageous  conditions  for  the  work  of  breaking  ore  and 
its  disposal  than  does  longwall  stoping,  the  working  face 
being  level  and  adjacent  to  a  larger  number  of  chutes  than 
is  the  case  with  any  other  method.  Further,  cars  or  wheel- 
barrows can  be  employed  to  advantage  in  handling  and 
distributing  both  ore  and  waste,  but  are  applicable  only 
when  the  stope  is  filled  with  waste  or  ore,  or  there  are  inter- 
mediate levels  built  on  stulls.  Irregularities  in  the  deposit, 
such  as  barren  portions,  seriously  interfere  with  the  work 
and  often  require  a  change  in  method. 


STOPING  AND  HANDLING  ORE  IN   STOPES  45 

METHODS  OF  HANDLING  ORE  IN  STOPES 

The  ways  and  means  employed  in  handling  ore  in  stopes 
are  almost  as  varied  as  the  methods  of  stoping,  and  in  fact  the 
handling  of  ore  in  the  working  places  often  has  a  controlling 
influence  on  the  methods  of  extracting  the  mineral.  As  the 
methods  of  stoping  are  fundamental  operations  in  the  extrac- 
tion of  ores,  so  in  like  manner  the  methods  of  handling  the 
ore  in  the  usual  stoping  operations  are  similar  to  all  other 
methods  in  use  regardless  of  what  kind  of  mineral  or  metal 
is  mined  or  how  it  is  mined. 

From  the  standpoint  of  handling  ore  the  work  may  be 
divided  into  two  classes  as  in  open  and  closed  stopes.  The 
former  comprises  the  simplest  class  of  work,  while  the  latter 
is  by  far  the  most  important  both  as  to  kinds  and  extent 
of  operations. 

Open  stope  work  may  include  practically  all  methods  of 
stoping,  but  is  usually  applied  to  moderate  inclinations  and 
especially  such  that  the  broken  ore  will  move  downward  by 
gravity  with  or  without  assistance.  The  best  results  are 
secured  when  the  deposit  dips  at  an  angle  of  38  to  40°,  or 
is  equal  to  the  angle  of  repose  of  the  broken  ore.  With  a 
fairly  even  footwall  or  floor  standing  at  a  proper  angle, 
ore  can  be  readily  transferred  for  a  distance  of  several 
hundred  feet,  and  that  too  regardless  of  whether  overhand 
or  underhand  stoping  is  done. 

On  reaching  the  bottom  of  the  stope  the  ore  is  either 
shoveled  into  cars  standing  on  the  level  tracks  or  may  be 
run  on  to  docks  from  which  it  is  shoveled  into  cars.  The 


46  ORE  MINING  METHODS 

latter  method  is  preferable  from  the  standpoint  of  shoveling, 
but  is  not  as  extensively  employed  as  the  former.      (See 

Fig.  50 

When  the  footwall  is  somewhat  uneven,  or  the  dip  is 
several  degrees  less  than  the  angle  of  repose  of  the  ore,  it 
may  be  found  to  be  necessary  to  assist  gravity  in  the  trans- 
ference of  the  ore  either  by  actually  shoveling  .or  raking,  or 
by  placing  it  in  chutes  of  wood  or  metal,  the  angle  of  which 
is  greater  than  that  of  the  stope  floor,  or  the  friction  less  than 
that  between  the  ore  and  stope  floor. 

Shoveling  is  still  largely  employed  in  certain  districts 
and  with  both  overhand  and  underhand  work.  Sheets  of 
boiler  plate  may  be  laid  on  the  stope  floor  as  in  coal  mining, 
extending  from  the  bottom  of  the  stope  to  the  working  face, 
the  sheets  overlapping  shingle-fashion.  Better  still  is  the 
use  of  curved  sheet-metal  chutes,  which  may  be  placed 
similarly  to  the  plain  sheets,  but  are  easier  to  handle  and 
consequently  more  care  is  usually  taken  in  mounting  them 
with  regard  to  both  direction  and  inclination.  Stopes  with 
inclinations  falling  to  as  much  as  15°  below  the  angle  of 
repose  may  have  the  ore  handled  without  difficulty  by  such 
means.  In  order  that  the  momentum  of  the  ore  may  be 
checked  somewhat  before  entering  the  car  at  the  bottom  of 
the  stope,  it  is  customary  to  materially  reduce  the  slope  of 
the  last  two  or  three  sections  of  chute.  (See  Fig.  10.) 

The  use  of  metal  chutes  may  be  extended  to  stopes  of 
very  slight  dip  by  giving  them  a  shaking  motion,  while 
the  monorail  and  chain  conveyors  are  now  being  employed 
to  transfer  mineral  for  considerable  distances  in  mines  and 


STOPING  AND  HANDLING   ORE  IN   STOPES 


47 


48  ORE  MINING  METHODS 

under   practically  all  degrees  of  inclination,  even  reverse 
grades. 

A  unique  method  of  overcoming  an  exceedingly  rough 
and  irregular  floor  of  stope  is  that  in  use  in  the  North  Star 
mines,  Grass  Valley,  California.  The  gravity  plane  idea 
as  employed  in  coal  mines  has  been  adopted.  A  double  line 
of  track  is  laid  directly  up  the  dip  of  the  stope  at  the  upper 
end  of  which  is  set  a  post  to  which  is  attached  a  three- wheeled 
device  called  a  'go-devil.'  A  steel  cable  passes  from  the 
bottom  to  the  top  of  the  plane,  being  attached  to  an  empty 
car  below  and  after  passing  around  the  three  grooved  wheels 
of  the  go-devil  extends  and  is  attached  to  a  loaded  car  at  the 
top  of  the  plane.  The  go-devil  is  controlled  by  a  hand- 
lever,  and  when  pushed  off  the  landing  the  loaded  car  runs 
to  the  level  below,  drawing  up  the  empty  car.  This  system 
has  proved  very  successful  and  is  extensively  employed  in 
these  mines. 

In  deposits  of  slight  inclination,  where  breast  stoping  is 
employed,  cars  are  run  to  the  face  on  track  laid  diagonally 
up  the  stope  and  maintaining  a  grade  such  that  the  cars 
can  be  controlled  by  brakes  or  sprags.  The  character  of 
the  ore  has  an  important  bearing  upon  the  distance  that  the 
ore  will  travel  from  the  face  on  blasting  it  down.  This  can 
be  illustrated  to  good  advantage  by  citing  the  conditions 
existing  in  the  hard  iron  ore  mines  of  the  Birmingham  dis- 
trict, Alabama.  To  a  certain  depth  below  the  outcrop  the 
ore  has,  in  many  places,  been  rendered  more  or  less  soft  by 
percolating  waters;  below  this  point  the  ores  are  still  hard. 
Stopes  carried  on  moderate  inclinations  in  the  hard  ore  will 


STOPING  AND   HANDLING   ORE   IN   STOPES 


49 


50  ORE  MINING  METHODS 

deliver  a  large  part  of  the  ore  at  the  bottom  of  the  stope,  as 
it  breaks  coarse  and  rolls  well;  with  the  soft  ore  the  reverse 
is  the  case;  the  ore,  breaks  moderately  fine  and  slumps  down 
close  to  the  working  face,  necessitating  the  employment  of 
cars  thoughout  the  stope.  (See  Fig.  n.) 

Closed  stope  work  as  distinguished  from  open  stope  work 
has  the  levels  roofed  over  and  protected  by  pillars  of 
mineral,  by  stulls  and  lagging  covered  in  turn  with  waste, 
by  pack-walls,  etc.  In  wide  veins  or  massive  deposits 
the  levels  may  be  protected  by  sets  and  square-sets  held 
in  place  by  stulls,  filling,  etc.  (See  Figs,  i  and  2.)  In 
either  case  connection  is  made  between  the  levels  and  open 
stopes  by  passages  commonly  known  as  chutes,  mill-holes, 
passes,  etc. 

In  both  overhand  and  underhand  stoping,  pillars  are 
occasionally  left  directly  above  the  levels  which  serve  the 
double  purpose  of  support  and  protection  to  the  levels. 
Holes  called  i block  holes'  are  cut  through  these  pillars  at 
intervals  of  25  feet  or  more,  the  ore  being  passed  through 
them  to  the  cars  below.  (See  stope  B-i,  Fig.  6.)  A  line 
of  stulls  may  be  employed  in  place  of  pillars  and  serves  the 
same  purpose.  On  moderately  flat  dips,  and  where  there 
is  little  or  no  waste  to  be  disposed  of,  the  ore  may  be  trans- 
ferred to  the  bottom  of  the  stope  as  in  open  stopes,  the 
advantages  being  that  the  levels  are  not  cumbered  by  ore 
running  down  from  the  stope  above  and  that  the  cars  are 
loaded  by  gravity. 

When  stulls  are  used  the  line  of  stulls  and  covering  of 
lagging  may  at  intervals  be  extended  in  a  diagonal  direction 


STOPING  AND   HANDLING   ORE  IN   STOPES  51 

for  some  distance  up  the  stope,  meeting  similar  lines  run  in 
opposite  directions.  This  arrangement  is  called  '  winged 
stulls'  and  is  useful  in  collecting  the  ore  sliding  downward 
and  in  delivering  it  to  the  chute  gates  extending  through 
the  line  of  stulls.  (See  Fig.  12.)  By  this  arrangement 
chutes  may  be  placed  further  apart. 

In  stopes  where  a  filling  of  waste  or  ore  is  employed,  built- 
up  chutes,  consisting  of  either  walled-up,  well-like  openings, 
cribbed  passages,  or  passages  one  side  of  which  is  wall-rock 
(usually  footwall),  the  other  sides  timber,  are  extended 
through  the  filling  to  the  stope  above.  These  passages, 
usually  the  timbered  ones,  are  made  with  two  compartments 
-  one  for  ore,  the  other  for  a  manway. 

In  narrow  veins  the  chutes  usually  follow  the  dip  very 
closely  and  are  often  built  on  the  footwall,  while  in  wider 
veins  they  may  be  vertical  or  inclined  at  whatever  angle 
seems  best  suited  to  the  character  of  the  ore  and  the  chute 
lining.  In  vertical  chutes  of  small  section  there  is  danger 
of  their  becoming  choked  up,  requiring  the  use  of  explosives, 
which  must  be  used  with  care  to  prevent  damage  to  chute 
walls.  Broken-sloped  chutes  are  preferable  when  long  lines 
must  be  employed.  The  branched  chutes  occasionally  used 
with  square-sets  in  the  mines  of  the  Cceur  d'Alene  District 
are  good  examples  of  broken-sloped  chutes.  Several  por- 
tions of  a  stope  may  be  served  by  branches  extending  at 
various  angles  and  in  a  number  of  directions  from  the  main 
chute,  and  the  movement  of  ore,  especially  in  steep  chutes, 
can  be  controlled  to  better  advantage  by  their  use.  Broken- 
sloped  chutes  driven  in  solid  ground  are  found  to  give  better 


ORE  MINING  METHODS 


<u 

O 

bJD 
G 


STOPING  AND  HANDLING  ORE  IN  STOPES  53 

results  when  the  first  portion  above  the  point  of  delivery  of 
ore  is  vertical,  the  remaining  portion  standing  at  an  angle 
of  30°  or  more  from  the  vertical.  It  is  claimed  for  such 
chutes  that  the  change  in  direction  prevents  packing  of  ore 
and  choking  of  chutes.  This  arrangement  is  shown  in  the 
vertical  section  of  the  caving  system  employed  in  the  B ing- 
ham  Canyon  mines. 

At  the  lower  end  of  the  chutes  must  be  some  device  not 
only  for  directing  the  ore  into  cars  but  for  controlling  the  flow 
of  ore  from  the  chutes.  This  is  accomplished  by  having  a 
sloping  spout  attached  to  the  bottom  of  the  chute,  provided 
with  a  gate  and  controlled  by  a  hand  lever.  Unless  con- 
structed of  proper  section  and  given  a  suitable  slope  the  ore 
will  become  jammed  in  and  will  not  discharge.  A  method 
of  discharging  ore  from  stopes,  often  used  in  the  Australian 
mines,  goes  by  the  name  of  ' chinaman.'  The  chinaman 
consists  of  a  platform,  built  several  feet  below  the  line  of 
stulls,  containing  a  number  of  openings  through  which  ore 
is  discharged  into  cars  below.  An  opening  in  the  lagging 
permits  the  ore  to  flow  from  the  stope  on  to  the  platform, 
where  it  piles  up  until  the  opening  in  the  stull  lagging  is 
reached.  On  removing  the  covers  to  the  platform  openings 
the  ore  falls  into  the  cars,  and  when  a  certain  amount  has 
been  drawn  off  a  movement  of  the  ore  in  the  stope  again 
takes  place.  The  flow  of  ore  from  the  stope  is  then  auto- 
matically controlled  by  the  operation  of  loading  cars.  (See 

Fig.  13-) 

Handling  ore  at  the  working  face  may  be  done  by  hand, 
i.e.,  by  shoveling,  but  when  this  is  the  practice  the  chutes  or 


54 


ORE  MINING  METHODS 


mill-holes  must  be  placed  closer  together  and  should  not 
exceed  25  feet  apart.  In  wide  veins  where  the  stopes  are 
large,  wheelbarrows  may  be  employed,  also  cars;  in  which 
case  the  chutes  may  be  spaced  much  further  apart,  as  from 
35  to  55  feet. 


FIG.  13.  —  A  Chinaman  Chute  as  used  in  Australian  Mines. 

Other  devices  might  be  described  and  cases  cited  illus- 
trating the  use  of  chutes  and  loading  mechanisms,  but  those 
given  will  serve  to  show  the  general  methods  of  procedure 
and  the  importance  of  efficient  methods  of  handling  ore. 


CHAPTER  III 

MINING    IN    NARROW    VEINS    AND    BEDDED 
DEPOSITS 

INTRODUCTION 

As  the  methods  of  breaking  down  ore  or  stoping  have 
already  been  discussed  and  their  relation  to  the  handling  of 
ore  in  the  working  places  and  the  development  work  of  the 
mine  has  been  indicated,  the  methods  of  mining  considered 
in  a  general  way  may  now  be  taken  up.  Mining  is  the 
working  of  mineral  deposits  and  includes  all  phases  of  work 
pertaining  thereto,  as  prospecting,  development,  exploration 
and  extraction  of  ore.  Methods  or  systems  of  mining,  as 
generally  considered,  consist  of  the  development  and  work- 
ing of  deposits,  but  by  common  usage  the  meaning  of  the 
terms  has  been  extended  and  now  includes  the  working  of 
deposits  and  support  of  workings.  The  expressions  over- 
hand and  underhand  mining,  square-set  mining,  the  top 
slice  and  sub-drift  cavings  systems  of  mining,  etc.,  illustrate 
the  indefiniteness  of  such  a  designation  as  method  or  sys- 
tem, but  it  must  be  admitted  indicate  the  salient  features 
of  the  work  done,  and  at  the  same  time  are  probably  less 
cumbersome  than  other  more  exact  and  discriminating  desig- 
nations. 

In  the  following  pages  are  given  methods  of  mining  appli- 
cable to  narrow  and  moderately  narrow  veins  and  bedded 

55 


£6  ORE  MINING  METHODS 

deposits  and  they  are  considered  in  order  of  their  simplicity 
and  ease  of  working.  The  following  methods  are  discussed : 
mining  bedded  deposits  by  the  use  of  props;  mining  mineral 
veins  by  the  use  of  stulls;  mining  mineral  veins  by  the  use 
of  square-sets;  mining  mineral  veins  by  the  use  of  filling; 
and  mining  veins  and  bedded  deposits  by  caving. 

An  endeavor  has  been  made  to  limit  the  discussion  of 
methods  of  mining  in  this  chapter  to  veins  and  deposits  not 
exceeding  35  to  40  feet  in  width  and  particularly  to  much 
narrower  ones,  but  it  has  been  found  difficult  to  do  this.  A 
few  descriptions  are  given  of  deposits  averaging  35  feet  and 
under,  where  good  descriptions  of  narrower  veins  were  not 
available  from  the  writer's  personal  experience  or  from 
technical  literature. 

MINING  BEDDED  DEPOSITS  BY  THE  USE  OF  PROPS 

The  iron  mines  of  the  Birmingham  district,  Alabama, 

are  good  illustrations  of  the  application  of  overhand  stoping 

to  bedded  deposits  of  slight  and  moder- 

1.  Birmingham,  Ala. 

2.  iron  ore.  ate  inclinations.     The  strata  worked  vary 

3.  Bedded  deposit. 

4.  Thickness  10  to    from  io  to  2o  odd  feet  in  thickness,  while 

20  feet. 

the  dip  ranges  from  8  to  50  and  above, 
but  averages  about  12°.  The  ore  occurs  in  the  Clinton 
formation  of  the  Red  Mountains;  it  is  hematite  and  was 
originally  very  hard,  but  owing  to  the  leaching  action  of 
percolating  waters  the  upper  portions  have  been  changed 
more  or  less  into  a  soft  ore,  due  probably  to  the  loss  of  lime. 
The  irregularity  of  the  limit  of  soft  ore  is  shown  in  Fig.  14. 


MINING  IN  NARROW  VEINS  AND   BEDDED   DEPOSITS     57 

The  formations  overlying  the  iron  are  largely  sandstone, 
while  shale  occurs  below. 

These  mines  are  opened  by  slopes  or  inclined  shafts  in 
the  deposit,  from  which  at  intervals  of  50  to  60  feet  levels  are 
driven.  The  levels  are  run  at  a  width  of  12  to  15  feet  for  a 
distance  of  100  to  150  feet,  beyond  which  point  they  are 
increased  to  20  or  30  feet,  forming  low  stopes.  On  both 
sides  of  the  shaft,  pillars  are  left  which  vary  in  width  from 
60  to  75  feet.  The  width  of  the  pillars  is  definitely  deter- 
mined by  air-ways  and  man-ways  which  parallel  the  shaft. 
Along  the  line  of  the  stopes  break-throughs  are  formed,  mak- 
ing connection  between  two  adjacent  stopes,  and  serve  as 
means  of  inlet  and  exit  to  and  from  the  stopes  as  well  as  a 
convenience  in  carrying  air  lines  to  all  parts  of  them;  ventila- 
tion is  also  facilitated. 

The  stopes  having  been  driven  to  the  limit  of  economic 
handling  of  ore  on  the  levels,  the  direction  of  working  is 
reversed  and  the  ore  left  standing  in  pillars  during  the  first 
part  of  the  operations  is  now  removed.  The  method  of 
mining  then  resolves  itself  into  room-and-pillar  work  by 
advancing  and  retreating,  the  larger  part  of  the  ore  being 
mined  from  the  pillars  and  therefore  by  pillar-drawing.  The 
drawing  of  pillars  may  be  accomplished  by  cutting  off 
longitudinal  or  transverse  slices;  the  former  when  the  ore 
is  moderately  soft  and  the  stopes  are  high,  the  latter  when 
hard  or  moderately  hard  ore  is  worked  and  the  levels  are 
close  together. 

Hard  ore  breaks  up  into  relatively  large  pieces  which 
under  the  impulse  of  the  blast  readily  find  their  way  to  the 


ORE  MINING  METHODS 


I 
t 


MINING  IN  NARROW  VEINS  AND   BEDDED   DEPOSITS      59 

bottom  of  the  stopes;  while  the  soft  ore,  which  is  more  or 
less  earthy  in  character,  slumps  down  and  does  not  travel 
far  from  the  working  face.  It  is  evident  then  that  either 
the  levels  must  be  driven  closer  together  or  the  cars  must  be 
run  up  into  the  stopes  to  the  working  face;  in  fact  both 
methods  are  employed,  but  as  levels  cannot  be  run  too  close 
together,  even  if  formed  by  stoping,  as  it  is  an  expensive 
operation,  the  running  of  cars  into  the  stopes  is  usually 
preferred.  (See  Fig.  1 1 . ) 

With  low  dips  the  method  of  attack,  although  up  the 
dip,  as  in  overhand  stoping,  resembles  more  closely  breast 
stoping  and  has  all  the  advantages  of  such  work. 

Owing  to  the  comparatively  slight  inclination  of  the  de- 
posit practically  the  whole  weight  of  the  roof  must  be  sup- 
ported, therefore  necessitating  considerable  support,  which  is 
provided  by  an  extensive  use  of  props.  These  props  vary 
from  8  to  14  and  16  inches  in  diameter,  being  used  in  the 
rough,  and  are  spaced  from  6  to  25  feet  apart  according 
to  the  condition  of  the  roof.  The  drawing  of  pillars  in 
the  upper  levels  and  the  caving  that  results  relieves  the 
pressure  to  a  certain  extent  in  the  lower  levels,  but  with 
greater  depth  of  working  the  problem  of  support  will  be- 
come more  serious  and  may  require  a  change  in  the  method 
of  working. 

The  advantages  and  disadvantages  of  the  method  de- 
scribed above  have  already  been  given  under  the  respective 
heads  of  overhand  and  breast  stoping,  but,  as  previously 
indicated,  a  serious  disadvantage  is  the  high  cost  of  develop- 
ment resulting  from  running  levels  close  together,  but  it  is 


60  ORE  MINING  METHODS 

claimed  that  this  is  largely  offset  by  the  thickness  of  the 
workable  strata  and  the  large  outputs  obtained  from  small 
areas.  The  cost  of  timber  is  also  a  large  item. 

MINING  MINERAL  VEINS  BY  THE  USE  OF  STULLS 

Of  the  various  methods  of  maintaining  stopes  employed 

in  the  Tonopah  mines,  the  use  of  stulls  is    probably  the 

most  common.     Square-sets  are  also  em- 

1.  Tonopah  Mine, 

Nev.  ployed,  but  owing  to  the  cost  of  suitable 

2.  Gold  and  Silver. 

3.  Veins.  timber,  that  method  of  support  is  resorted 

4.  Width  8  to  10  ft. 

to  only  in  special  cases.  Owing  to  the 
value  of  the  ores,  which  ranges  from  $12.00  to  $50.00  a  ton, 
it  is  desirable  if  possible  to  remove  the  entire  mass  of  the 
vein-filling  and  often  a  part  of  the  wall-rock.  The  total 
extraction  of  the  ore  is  then  the  ultimate  aim  of  the  mining 
operations,  which  is  readily  accomplished  by  the  method 
employed,  being  overhand  stoping  by  the  use  of  stulls. 

The  ore  formation  consists  of  a  broad  belt  of  fissure  veins 
often  occurring  close  together.  The  deposits  occur  in  ande- 
site  either  as  fissure  or  contact  veins,  and  but  few  of  them 
reach  the  surface.  A  peculiar  feature  observed  in  working 
some  of  the  larger  veins  is  that  their  course  as  followed  on 
the  dip  is  broken  by  flats  and  pitches,  resembling  to  a 
marked  degree  a  huge  flight  of  stairs,  which  is  due  to  fault- 
ing. 

The  veins  are  opened  and  developed  by  vertical  shafts  and 
cross-cuts,  which  divide  the  deposits  into  lifts  lying  between 
levels  spaced  about  100  feet  apart.  In  the  Tonopah  Mine 
stopes  are  carried  up  the  full  width  of  the  vein,  the  walls 


MINING  IN  NARROW  VEINS  AND  BEDDED  DEPOSITS      61 


62  ORE  MINING  METHODS 

being  supported  by  stulls.  At  a  height  of  8  to  9  feet  above 
the  sill-floor  of  the  stope  a  row  of  stulls  is  placed  in  a  hori- 
zontal position  and  wedged  fast  between  the  walls.  In 
order  to  properly  support  the  horizontal  stulls  two  or  more 
posts,  depending  upon  the  width  of  the  vein,  are  set  up 
under  each  stull  and  upon  similarly  placed  sills  on  the  stope- 
floor.  When  lagging  has  been  placed  upon  the  horizontal 
stulls,  the  so-called  '  stull-floors '  are  formed.  (See  Fig.  15.) 
One  or  more  rows  of  ore  chutes  are  built  in  between  the 
stulls,  being  placed  on  both  sides  of  the  vein  or  on  one  side 
only,  the  number  and  arrangement  depending  upon  the 
width  of  the  vein.  A  chute  placed  at  one  side  of  the  stull- 
floor,  in  wide  veins,  necessitates  too  much  shoveling  of  ore 
in  finally  clearing  the  stopes.  Stoping  is  continued  upward, 
the  walls  being  supported  by  other  rows  of  stulls  spaced  from 
6  to  15  feet  apart  vertically,  depending  upon  conditions  of 
the  wall-rock.  These  stulls  also  serve  as  supports  for  lagging 
o'r  scaffoldings  upon  which  the  miners  stand  and  mount  their 
drills.  Owing  to  the  small  size  of  the  timbers  used,  which 
seldom  exceeds  8  inches,  and  the  increased  width  of  stopes 
in  many  places,  it  is  often  found  necessary  to  place  props  or 
struts  between  the  stulls  to  prevent  their  buckling  and 
breaking.  All  stulls  are  provided  with  blocking  called  '  stull 
headings'  which  increase  the  bearing  of  the  stulls  and  at 
the  same  time  afford  a  better  footing  for  them. 

A  stope  having  reached  the  level  above  and  been  broken 
through  into  it,  props  are  carefully  set  between  the  stope- 
sills  and  the  last  placed  stulls  in  the  stope  below,  thus  pro- 
viding a  fairly  strong  support  for  the  level  timbers  above. 


MINING  IN  NARROW  VEINS  AND   BEDDED  DEPOSITS     63 

No  stope  should  be  worked  out  and  connected  with  a  level 
above  until  the  upper  level  has  been  worked  and  the  ore 
drawn  off,  or  the  ore  should  be  drawn  off  practically  as  fast 
as  broken  in  order  that  undue  weight  may  not  be  thrown 
upon  the  stulls  supporting  the  levels.  (See  Fig.  15.) 

At  the  flatter  portions  of  the  veins  considerable  difficulty 
is  often  experienced  in  setting  the  stulls,  especially  the 
horizontal  ones,  and  consequently  square-set  timbering  is 
largely  employed  at  such  places;  greater  strength  is  also 
obtained. 

Filling  is  occasionally  used  in  connection  with  square- 
sets,  but  probably  to  a  greater  extent  with  stulls,  the 
empty  stopes  being  run  full  of  waste  rock,  which  can  be 
transferred  from  stope  to  stope  as  the  upper  levels  are 
exhausted. 

The  method  of  working  with  horizontal  and  inclined 
stulls  as  employed  in  the  Tonopah  mines  is  applicable  to 
narrow  and  moderately  wide  veins  of  high  dips  and  with 
fairly  strong  and  solid  walls.  While  it  might  be  employed 
in  working  low-grade  ores,  it  is  especially  suited  to  mod- 
erately high-grade  ores,  where  it  is  desirable  to  make  a 
high  percentage  extraction  of  ore. 

The  advantages  of  the  method  are: 

1.  The  complete  extraction  of  ore. 

2.  Use  of  relatively  small  timbers. 

3.  Ease  of  handling  ore. 

4.  Ready  access  to  the  stopes. 

5.  Ore  may  be  held  in  the  stopes  as  a  reserve. 

6.  Ventilation  is  good. 


64  ORE  MINING  METHODS 

The  disadvantages  of  the  method  are: 

1.  Use  of  considerable  timber,  which  is  expensive. 

2.  Confined  to  high  dips. 

3.  Lack  of  stability  of  workings  when  stopes  are  con- 
nected. 

4.  Stoppage  of  ore  chutes,  necessitating  blasting  out  the 
ore,  thus  injuring  chutes 

5.  Little  opportunity  to  sort  and  stow  waste  rock. 
The  application  of  overhand  or  back  stoping  to  veins  of 

variable  width  is  shown  to  advantage  in  the  Combination 

1.  combination        Mine>  Goldfield,  Nevada.     The  lodes  of  the 

Mine,  Goldfield,  Goldfield  district  consist  of  shattered  and 

2.  Gold  and  Silver,    fissured  zones  of  silification.     In  the  Com- 

3.  Veins  or  Zones. 

4.  Average  thickness  bination  Mine  the  vein  filling  as  well  as  the 

country-rock  is  altered  dacite.  Occasion- 
ally the  silicified  zones  extend  into  the  walls,  making  the 
width  of  the  workable  deposit  rather  indeterminate.  The 
width  of  the  silicified  zones  usually  does  not  exceed  50  feet, 
while  in  the  majority  of  cases  20  feet  is  a  fair  average.  As 
a  usual  thing  the  ground  is  easy  to  support  and  wide  stopes 
are  often  worked  without  fear  of  collapse. 

Referring  to  the  section,  Fig.  16,  it  is  seen  that  the  first 
level  was  formed  at  a  depth  of  80  feet,  two  drifts  being 
driven  in  the  deposit  to  the  limits  of  the  ore-shoot,  one  on 
either  side  of  the  lode.  By  cutting-out  stoping,  both  of  the 
stopes  were  increased  in  height  and  width  until  they  ran 
together  in  the  center  of  the  lode  and  at  the  same  time  were 
extended  to  the  walls  of  the  lode.  As  soon  as  sufficient 
height  of  stope  was  secured  to  permit  the  running  of  cars, 


MINING   IN  NARROW  VEINS  AND   BEDDED  DEPOSITS     65 


GLORY-HOLE 


I 

m^^^^^^S^A   ' 
w^lMSif&SM^m  < 

a  «Bi  ^ 


rt 

!_ 

<U 

"8 

% 

bfl 

c 
'5 


66  ORE  MINING   METHODS 

stulls  and  lagging  were  placed.  Subsequent  work  filled  the 
stope  with  broken  ore  which  was  drawn  off  as  desired  by 
chutes  spaced  every  20  feet  along  the  drifts.  The  width  of 
the  stope  was  increased  ultimately  to  50  feet  at  one  or  more 
points,  but  stood  without  support  by  carefully  arching  the 
back.  The  combined  stopes  were  raised  to  within  about 
15  feet  of  the  surface,  when  raises  were  put  up  breaking 
through,  the  remainder  of  the  arch  being  cut  out  by  under- 
hand work. 

In  the  meantime  a  second  level  was  driven,  as  shown,  at 
the  i3o-foot  level,  which  was,  however,  carried  the  full  width 
of  the  lode,  being  narrower  at  this  point  than  above,  and  was 
stulled  and  lagged  with  timbers  of  suitable  size.  The 
second  stope  was  raised  to  within  about  6  feet  of  the  8o-foot 
level,  and  raises  were  put  through  connecting  the  levels 
above  with  the  stope  below.  All  handling  of  ore  on  the  first 
level  was  then  abandoned  and  the  ore  from  the  upper  stope 
was  drawn  off  through  the  raises  connecting  the  stopes. 
As  the  ore  was  drawn  from  the  upper  stope  the  pillars  above 
the  levels  were  exposed  and  were  attacked  and  stoped-out, 
at  the  same  time  any  ore  exposed  on  the  walls  of  the  open 
stope  was  broken  down  and  ultimately  loaded  into  cars  on 
the  130-foot  level. 

The  third  level  was  formed  at  the  230-foot  point,  the 
ground  between  it  and  the  second  level  being  worked  by 
intermediate  levels  spaced  50  feet  apart,  especially  in  the 
weaker  ground,  as  in  the  sulphide  ores.  The  intermediate 
levels  are  permanently  timbered.  It  is  proposed  to  fill  the 
stopes  with  waste  after  the  ore  has  been  withdrawn. 


MINING  IN  NARROW  VEINS  AND   BEDDED  DEPOSITS     67 

This  particular  method  of  mining  is  applicable  to  veins  of 
varying  widths  and  dips,  as  widths  of  20  to  50  feet  and  dips 
of  30  to  90°  with  the  horizontal,  also  to  strong  and  moderately 
strong  ores  and  wall-rocks. 

The  advantages  of  this  method  are: 

1.  Little  timber  is  necessary. 

2.  The  ore  is  handled  with  little  labor. 

3.  By  opening  the  mine  to  the  surface  the  ore  in  the 
wall-rock  can  be  more  carefully  and  systematically  mined. 

4.  Ventilation  is  good. 

The  disadvantages  of  the  method  are: 

1.  Short  distance  between  levels  and  expense  of  forming 
a  number  of  levels. 

2.  A  possible  loss  of  high-grade  ore  by  breakage  in  draw- 
ing from  one  stope  to  another. 

3.  The  accumulation  of  water  in  workings  due  to  open- 
cuts. 

4.  The  necessity  of  using  long  stulls  and  consequently 
large  ones  on  those  levels  where  the  lode  is  wide. 

The  employment  of  stulls  in  veins  varying  in  width  from 
15  feet  and  over  is  shown  to  good  advantage  in  the  lead- 
silver  mines  of  the  Cceur  d'Alene  district, 

'    1.  The  Hecla  Mine, 

where  the  system  has  its  widest  application.  Burke,  Idaho. 

2.  Lead  and  Silver. 

The  veins  occur  in  slates  and  quartzites  3.  Veins, 
and  have  rather  high  angles  of  dip,  being  4'  Width  8  to  35  ft. 
not  far  from  70°  with  the  horizontal.    They  range  from  8  to 
15  even  up  to  35  feet  in  width,  the  walls  often  being  inde- 
terminate and  disintegrating  badly  on  exposure  to  the  air. 


68  ORE  MINING  METHODS 

The  ore  is  broken  by  overhand  stoping,  locally  known  as 
'back  stoping/  the  walls  and  back  of  ore  being  supported 
by  '  stull-sets '  and  filling.  (See  Fig.  17.) 

The  levels  are  usually  driven  250  to  300  feet  apart,  the 
stopes  being  opened  directly  off  the  levels  and  to  the  full 
width  of  the  vein.  The  supporting  stull-sets  are  built  up 
from  the  levels  and  are  kept  open  for  the  first  two  floors  for 
convenience  in  handling  timber,  after  which  they  are  usually 
filled  with  barren  material,  sorted  from  the  vein  during 
mining.  The  height  of  the  stull  posts  varies  in  the  different 
mines  from  6  feet  to  8  feet  3  inches,  making  the  distance 
between  floors  approximately  9  and  10  feet  respectively. 
The  size  of  the  stulls  and  posts  ranges  from  10  to  16  inches  in 
diameter.  Occasionally  the  stull-sets  are  reenforced  by  other 
sets  placed  below  them,  which  is  usually  done  on  the  second 
floor.  The  posts  of  the  stull-sets  are  usually  placed  from 
1 8  inches  to  3  feet  from  the  walls  in  order  to  allow  for  cutting 
off  the  ends  of  the  stulls  when  they  begin  to  break  and 
splinter  as  the  weight  of  the  walls  comes  more  upon  them. 
On  cutting  away  the  broken  ends  of  the  stulls  the  old  block- 
ing or  head  boards  are  removed,  the  walls  smoothed  up  and 
new  boards  placed,  the  whole  being  wedged  fast  again. 
The  stull-sets  are  spaced  about  8  feet  apart  along  the 
stope. 

Above  the  second  floor  and  on  top  of  the  stulls  long  tim- 
bers are  placed  running  longitudinally  with  the  stope,  upon 
which  in  turn  are  laid  other  timbers  but  extending  directly 
across  the  vein.  These  latter  timbers  or  sills  are  placed 
about  4  feet  apart,  and  when  covered  with  lagging  form  the 


MINING   IN  NARROW  VEINS  AND   BEDDED   DEPOSITS      69 


FIG.  17. —  Application  of  Stull-Sets  to  the  Mining  of  Medium-sized  Veins. 


70  ORE  MINING  METHODS 

floor  upon  which  the  waste-filling  is  placed.  The  lagging  is 
sawed  timber  3  by  12  inches  and  of  suitable  length  to  reach 
at  least  from  one  sill  to  another. 

An  open  space  is  maintained  around  the  ore  chutes,  man- 
ways  and  timber  slides  on  the  second  floor  of  each  level  by 
boarding  off  a  portion  of  the  stope.  In  narrow  veins  the 
boarded-up  partitions  extend  from  wall  to  wall,  while  in 
wider  veins  a  relatively  large  space  is  fenced  in.  (See  Fig. 
1 8.)  Room  is  thus  provided  for  handling  ore  and  timber  and 
for  the  passage  of  men  as  the  stope  increases  in  height. 
The  remaining  portion  of  the  vein  is  filled  in  with  waste 
and  is  commonly  known  as  the  ' corral.' 

The  waste-filling  is  carried  to  within  two  sets  of  stulls  or 
floors  of  the  face  or  back  of  the  stope,  the  floors  upon  which 
the  stoping  drills  are  mounted  consisting  of  lagging  placed 
upon  the  stulls.  This  lagging  is  removed  prior  to  placing 
the  filling,  and  is  used  over  and  over  again  as  the  stopes  in- 
crease in  height.  Temporary  supports  as  posts  are  placed 
between  the  stulls  and  back  of  stope  and  are  specially 
needed  in  wide  veins  and  heavy  ground. 

The  ore  as  broken  falls  upon  the  lagging  of  plank,  from 
which  it  is  shoveled  into  chutes,  the  waste  being  stowed  in 
the  corrals  below. 

The  stull-set  method  of  mining  is  applicable  to  highly 
inclined  deposits  varying  in  width  from  10  to  35  and  40 
feet.  It  is  possible  to  work  deposits  the  walls  of  which  are 
heavy  and  weak,  but  it  is  most  applicable  to  strong  walls 
and  ores  that  will  stand  well. 


MINING   IN  NARROW  VEINS  AND   BEDDED   DEPOSITS      71 


72  ORE  MINING  METHODS 

The  advantages  of  the  stull-set  method  are: 

1.  The  comparative  ease  of  handling  and  placing  timbers, 
the  number  of  pieces  being  less  than  employed  with  the 
square-set  method. 

2.  The  possibility  of  easing  up  the  timbers  and  repairing 
badly  broken  stulls.     Badly  broken  wall-rock  can  be  re- 
moved and  the  support  renewed  with  little  trouble. 

3.  Increased  height  of  stope  that  can  be  worked  even  in 
bad  ground. 

4.  Convenience  of  sorting  ore  and  storing  waste  with 
little  handling. 

5.  Safety  to  men,  numerous  means  of  escape  from  stopes 
being  provided. 

6.  Ventilation  in  stopes  is  good. 

7.  Large  percentage  extraction  is  possible. 
The  disadvantages  of  the  stull-set  method  are: 

1.  Considerable  timber  is  used  and  especially  large  sizes 
which  are  difficult  to  handle. 

2.  Method  is  limited  to  steep  dips  and  consequently  the 
stopes  must  be  carried  nearly  vertically. 

3.  The  difficulty  experienced  in  maintaining  the  large 
areas  of  open  stopes  both  horizontally  and  vertically. 

MINING  MINERAL  VEINS  BY  THE  USE  or  SQUARE-SETS 

Square-set  mining  is  extensively  used  in  the  Cceur  d'Alene 
lead-silver  district,  although  in  the  narrow  portions  of  the 
deposits  simple  posts  and  stulls  are  often  employed,  espe- 
cially if  the  roof  is  strong  and  firm.  The  application  of 
square-sets  to  the  wider  portions  of  the  deposits,  which 


MINING  IN  NARROW  VEINS  AND   BEDDED   DEPOSITS      73 

range  in  width  from  5  to  50  feet,  varies  both  with  the  dips 
and  the  character  of  the  ore.  The  older  method  consists 
in  overhand  stoping  the  deposit  in  hori-  ±  The  Bunker  Hiii- 
zontal  floors,  the  stopes  being  filled  with  wlrdner,  Waho. 
square-sets  as  rapidly  as  space  is  pro-  |;  VefnSand  Silver' 
vided  for  them.  The  more  recent  method  4'  Width  5  to  50  ft' 
differs  mainly  from  the  earlier  method  in  that  the  working 
face  is  carried  normal  to  the  foot-wall  or  as  nearly  so  as 
possible.  The  object  of  this  method  of  procedure  is  to 
transfer  the  weight  of  the  ore  largely  from  the  square-sets 
to  the  foot- wall. 

The  method  of  stoping  in  horizontal  floors  represents 
extensive  practice  in  the  working  of  metalliferous  mines  in 
all  parts  of  the  world,  being  applicable  to  both  fairly  steep 
and  slightly  dipping  veins.  In  the  Cceur  d'Alene  district  it 
has  been  successfully  employed  in  lodes  dipping  from  35  to 
70°.  The  square-sets  are  usually  9  by  5  by  6  feet,  i.e.,  the 
posts  are  9  feet,  the  girts  5  feet  and  the  caps  6  feet  long. 
(See  Fig.  19.) 

The  veins  are  usually  opened  by  tunnels,  although  a  few 
shafts  are  employed  where  conditions  permit;  however, 
regardless  of  how  opened,  the  actual  development  of  the 
ore  bodies  is  by  shafts,  either  extending  from  the  surface 
or  beginning  underground  as  winzes,  the  levels  being  driven 
from  them  to  the  deposit.  In  the  deposits,  especially  in  the 
wider  veins,  two  passages  are  usually  maintained  through 
the  timbered  stopes,  which  is  mainly  for  the  convenience 
of  handling  the  ore.  Two  sets  of  timbered  chutes  and 
an  occasional  man-way  extend  from  the  open  stope  above 


74 


ORE  MINING   METHODS 


MINING  IN  NARROW  VEINS  AND   BEDDED  DEPOSITS     75 

to  the  passages  below,  thus  maintaining  as  nearly  as 
possible  equal  convenience  in  handling  ore  across  the 
vein.  The  stopes  are  kept  filled  to  within  about  one  set 
of  the  top,  thus  providing  ample  support  to  the  walls  and 
roof  as  well  as  space  to  work  in  and  protection  to  the 
miners. 

As  previously  indicated,  where  the  ore  is  weak  and  heavy, 
throwing  much  weight  upon  the  square-sets,  the  more 
recent  method  of  carrying  the  working  face  normal  to  the 
foot- wall  is  now  being  successfully  employed. 

The  development  work  is  similar  in  both  methods  of 
working,  and  while  two  haulage-ways  may  be  maintained 
through  the  timbered  stopes,  the  same  advantage  may  be 
secured,  so  far  as  handling  ore  in  the  stopes  is  concerned,  by 
employing  branched  chutes.  The  branch  chutes  may  be 
attached  to  the  main  chutes  at  any  desired  point  before 
the  filling  is  placed,  the  slope  of  the  chute  being  carefully 
maintained  in  order  to  insure  positive  and  rapid  transfer- 
ence of  ore  from  the  face  to  the  loading  chute  below.  Ore 
chutes  are  placed  from  15  to  30  feet  apart,  while  the  man- 
ways  are  50  feet  apart. 

In  stoping,  the  face  is  attacked  next  to  the  hanging-wall 
and  the  excavation  is  supported  by  placing  sets  as  soon  as 
room  is  made  for  them.  The  work  of  cutting  out  the  in- 
clined slice  then  proceeds  downward  until  the  foot-wall  is 
reached,  the  placing  of  sets  following  the  excavation.  This 
operation  is  repeated  until  the  desired  height  of  stope  is 
reached,  when  work  on  a  new  level  is  begun.  (See  Fig.  20.) 
Filling  is  drawn  from  old  stopes  and  from  drifts  driven  into 


76 


ORE  MINING   METHODS 


MINING  IN  NARROW  VEINS  AND   BEDDED  DEPOSITS     77 

the  hanging- walls  and  is  usually  kept  within  one  set  of  the 
face. 

The  application  of  square-sets  in  mining  as  a  means  of 
support  has  previously  been  pointed  out,  but  the  latter 
of  the  two  methods  described  above  illustrates  how  their 
usefulness  may  be  extended  under  particularly  difficult 
conditions. 

MINING  MINERAL  VEINS  BY  THE  USE  or  FILLING 

The  application  of  filling  to  the  working  of  the  gold  mines 
of  Zaruma,  Ecuador,  is  somewhat  unique  in  that  instead  of 
placing  the  filling  in  horizontal  floors  it  is 

1.   Zaruma,  Ecuador, 

run  in  from  above  and  stands  at  its  natural          S.  A. 

*         e  »      rni  -2.   Gold  Ore. 

"  angle  of  repose.  The  vein-matter  is  3  Vein> 
quartz  bearing  considerable  quantities  of  4.  Maximum  width 
finely  disseminated  pyrites,  and  bunches  of 
galena  and  blende  next  to  the  hanging-wall.  The  wall-rock 
is  diorite.  The  vein  is  faulted  by  an  extensive  fault-plane 
which  lies  within  the  vein  and  on  the  contact  of  foot- 
wall  and  vein-matter.  Owing  to  the  extensiveness  of  the 
movement,  a  very  heavy  gouge  occurs  which  ranges  be- 
tween 3  and  4  feet  in  thickness  and  is  extremely  weak  and 
treacherous.  The  value  of  the  ore  is  between  $4  and  $15 
per  ton. 

In  developing  the  ore-body  the  levels  are  run  in  the  foot- 
wall  at  a  distance  of  some  20  feet  from  the  vein,  from  which 
cross-cuts  are  driven  every  65  feet,  connecting  the  levels 
with  the  deposit.  From  the  various  points  of  attack  pro- 
vided by  the  cross-cuts  entering  the  ore-body  stoping  is 


78  ORE  MINING  METHODS 

begun,  being  carried  the  full  width  of  the  vein  and  to  a 
height  of  about  8  feet.  (See  Fig.  21.) 

Connection  is  made  between  the  levels  and  the  surface 
by  means  of  a  number  of  raises  along  the  footwall 
through  which  waste  rock  is  introduced  into  the  stopes. 
Beginning  at  the  raises  the  ore  is  cut  out  by  overhand  stoping, 
the  ore  being  cleared  away  as  rapidly  as  possible  and  hauled 
through  the  cross-cuts  and  levels  to  the  main  shaft.  When 
the  stopes  have  been  carried  as  high  as  is  considered  safe, 
filling  is  thrown  down  the  raises  until  the  stopes  are  nearly 
filled;  the  work  of  stoping  is  then  resumed,  but  to  prevent 
the  mixing  of  ore  and  waste  rock,  slabs  of  wood  are  placed 
upon  the  sloping  sides  of  the  filling.  This  operation  is 
repeated,  each  slice  being  carried  as  far  as  is  considered 
safe  and  then  filling  run  in  to  support  the  walls  and  bring 
the  footing  for  the  drills  sufficiently  close  to  the  working 
face.  Further,  temporary  supports,  as  posts,  may  be  set  up 
between  the  face  and  the  filling  as  occasion  demands.  The 
filling  run  in  from  above  distributes  itself  evenly  in  the 
stopes  without  extra  handling,  and  as  the  work  of  stoping  is 
carried  on  from  the  slope  of  the  filling  the  stope  face  must 
of  necessity  be  maintained  parallel  with  the  slope  of  the  fill- 
ing, which  is  practically  that  of  the  angle  of  repose  of  the 
waste  rock,  but  slightly  less  owing  to  the  miners  working 
upon  the  filling. 

In  the  course  of  time  the  various  stopes  run  together  and 
at  points  midway  between  the  raises,  or  at  the  intermediate 
cross-cuts.  At  these  points  cribbed  chutes  are  begun  and 
built  upward  as  the  work  of  stoping  and  filling  proceeds. 


MINING  IN  NARROW  VEINS  AND   BEDDED  DEPOSITS     79 


Cribbed  man-ways  are  maintained  through  the  center  of 
the  stopes  to  provide  means  of  ingress  and  egress  to  and  from 
the  stopes. 

The  method  of  filling  employed  at  the  Zaruma  mines  is 
applicable  to  moderately  wide  deposits  of  solid  and  firm  ore 


8o  ORE  MINING  METHODS 

but  not  overly  strong  walls.    The  method  is  usually  desig- 
nated as  'rill  stoping.' 
The  advantages  of  the  method  are: 

1.  Little  timber  is  required. 

2.  Levels  may  be  placed  a  considerable  distance  apart. 

3.  There  is  a  minimum  amount  of  handling  of  ore  and 
waste-filling. 

4.  Filling  can  be  carried  close  to  the  face,  as  it  does  not 
have  to  be  distributed. 

5.  Ventilation  is  good. 

The  disadvantages  of  the  method  are: 

1.  The  inconvenience  of  working  on  a  sloping  bank  of 
filling. 

2.  Loss  of  ore  by  mixing  with  waste. 

3.  Stoppage  of  all  work  in  a  stope  while  running  in  filling. 

4.  Little  opportunity  to  sort  ore  in  stopes. 

A  variety  of  methods  of  mining  is  to  be  found  in  use  in 
the  copper  mines  of  Butte,  Montana,  some  of  the  more 

1.  St.  Lawrence  Mine,  imP°rtant  °f  whkh  are:  the  US6  °f  Stulls 

Butte,  Mont.       an(j    lagging,  with    or    without    filling; 

2.  Copper  Ore. 

3.  Vein.  square-set    timbering,  with    or    without 


4.  ..  without 


timbering,  known  as  '  back-filling/ 

The  width  of  the  veins  worked  by  this  method  varies  from 
8  to  50  feet  and  dip  at  fairly  high  angles,  although  that  is 
not  a  requisite.  The  country  rock  is  granite,  which  is 
usually  fairly  strong  and  solid,  standing  well.  The  vein- 
matter  is  quartz  with  pyrite  and  copper  minerals. 

The  deposits  are  developed  by  vertical  shafts  from  which 


MINING  IN  NARROW  VEINS  AND   BEDDED  DEPOSITS     8 1 

cross-cuts  are  driven  to  the  veins  at  intervals  of  200  feet, 
levels  being  run  in  the  veins.  Stopes  may  be  opened  directly 
off  the  levels,  or  pillars  may  be  left  immediately  above  the 
levels;  in  the  former  case  the  filling  introduced  into  the  stopes 
to  support  the  walls  is  held  in  position  by  stulls  set  along  the 
levels,  while  in  the  latter  case  a  much  more  durable  and 
satisfactory  support  for  the  filling  is  provided  by  the  pillars. 
In  either  case  the  stopes  are  carried  horizontally  or  the  work 
of  cutting  out  the  ore  is  done  by  longwall  stoping.  (See 
Fig.  22.)  Preparatory  to  stoping  and  before  the  stopes 
have  been  more  than  opened,  waste  chutes  are  formed  in  the 
foot-wall  connecting  both  levels  and  stopes  and  are 
spaced  80  to  100  feet  apart  along  the  vein.  Ore  chutes  and 
man-ways,  built  up  from  the  levels,  are  carried  upward 
along  the  foot-wall  as  the  stopes  increase  in  height,  being 
strongly  timbered.  The  ore  chutes  are  usually  placed  at 
2 5 -foot  intervals,  while  the  man- ways  are  100  to  125  feet 
apart.  It  is  customary  to  build  two-compartment  passages, 
an  ore  chute  and  a  man-way  when  the  two  come  together, 
which  saves  time  and  expense. 

Beginning  at  a  raise  or  winze  cut  in  the  vein,  stopes  are 
worked  laterally  from  it,  being  carried  from  12  to  14  feet 
high  and  the  full  width  of  the  vein.  As  rapidly  as  the 
broken  ore  can  be  cleared  from  the  stope  by  shoveling  it 
into  the  ore  chutes,  waste  is  run  in,  filling  the  stope  to  a 
depth  of  about  8  feet,  being  distributed  by  a  limited 
amount  of  shoveling.  Distribution  of  waste  is  done  largely 
by  cars  running  between  waste  chutes.  The  ore  chutes  are 
timbered  up  and  kept  above  the  level  of  the  filling.  A 


82 


ORE   MINING  METHODS 


I     STORE       -WHwaaa^  IT/ l§ 


FIG.  22. —  Elevation  and  Plan  of  Stopes.     Back-filling  Method. 


MINING  IN  NARROW  VEINS  AND   BEDDED   DEPOSITS     83 

space  of  4  to  6  feet  is  maintained  between  the  filling  and 
the  back  of  the  stope,  which  provides  room  for  handling 
the  waste  in  cars.  As  the  filling  is  carried  on  back  of  the 
working  face  of  the  stope  this  particular  method  of  han- 
dling it  is  known  as  'back-filling/  and  when  employed  in  a 
mine  the  method  of  mining  is  commonly  spoken  of  as 
the  '  back-filling  method/  Subsequent  stoping  is  carried 
on  in  a  manner  similar  to  that  of  the  initial  work,  the 
stopes  being  from  12  to  14  feet  high,  and  the  successive 
layers  of  filling  placed  are  8  feet  thick.  By  this  arrange- 
ment of  parts  the  stopes  where  work  is  being  done  are 
12  to  14  feet  high,  while  the  space  between  filling  and 
stope-back  is  maintained  at  a  fairly  uniform  height  of  4  to 
6  feet. 

The  back-filling  method  is  usually  not  employed  except 
in  strong  or  moderately  firm  ground,  but  occasionally  ground 
is  worked  that  is  so  weak  that  props  must  be  used.  Usually 
no  attempt  is  made  to  draw  the  props  prior  to  blasting,  but 
they  are  pulled  out  of  the  broken  ore  as  it  is  shoveled  up. 
Comparatively  few  of  the  props  are  reused  as  supports  for  the 
back,  but  are  employed  in  building  chutes:  In  order  to 
prevent  loss  of  ore  from  mixing  with  the  waste-filling  during 
blasting  a  platform  or  mat  of  plank  is  placed  on  the  filling. 
Planks  or  'floor-boards7  for  this  purpose  are  2  by  8  to  12 
inches  and  are  cut  in  8-foot  lengths.  Shoveling  is  materially 
facilitated  by  the  use  of  such  platforms,  which  are  advanced 
with  the  stoping  face.  That  there  may  not  be  an  undue 
amount  of  shoveling  of  waste,  the  tracks  upon  which  the 
cars  carrying  the  filling  operate  are  frequently  shifted  from 


84  ORE  MINING  METHODS 

one  wall  to  the  other,  the  filling  being  run  in  to  place  rather 
than  shoveled. 

Stopes  may  be  completely  worked  out  by  this  method, 
but  it  is  the  usual  practice  to  leave  an  arch  pillar  of  12  to 
1 6  feet  thickness  between  the  stopes  and  the  levels.  (See 
Fig.  22.) 

The  back-filling  method  is  applicable  to  high  and  moder- 
ately high  dipping  veins.  The  wall-rock  and  ore  should  be 
fairly  strong  and  practically  self-supporting,  although  the 
use  of  props  is  common. 

The  advantages  of  the  method  are: 

1.  Under  favorable  conditions  little  or  no  timber  is  re- 
quired for  support. 

2.  Levels  are  far  apart,  reducing  the  amount  of  develop- 
ment work. 

3.  The  working  face  is  always  close  enough  for  thorough 
inspection. 

4.  There  is  little  danger  of  accidents. 

5.  Large  outputs  are  possible. 

6.  Ore  can  be  sorted  and  waste  stowed  in  stopes. 

7.  Ventilation  is  good. 

The  disadvantages  of  the  method  are: 

1.  Applicable  only  to  veins  having  strong  or  fairly  strong 
walls  and  ore. 

2.  Difficulty  and  expense  of  forming  waste  chutes. 

3.  Loss  of  ore  remaining  in  pillars. 

4.  Considerable  handling  of  ore  and  waste-filling. 


MINING  IN  NARROW  VEINS  AND  BEDDED  DEPOSITS     85 

The  method  of  mining  employed  in  the  copper  mines  of 
the  Lake  Superior  region  is  overhand  stoping  with  slight 
modifications  in  handling  ore  due  to  vary-  j  Baltic  and  Tri_ 
ing  inclinations  of  lodes.  The  dip  of  the  Mi^VMich* 
lodes  ranges  from  35  to  70°  in  the  various  c^^.  Ore 
mines.  In  those  lodes  where  the  steeper  3.  Vein. 

,.  .,          ,       ,  ,,  .   ,  ^      r     .        4.   Width  24  to  36  ft. 

dips  prevail  and  where  the  weight  of  the 
walls  is  consequently  less,  as  in  the  mines  of  the  Copper 
Range  Consolidated,  a  comparatively  new  method  of  mining 
has  recently  been  adopted,  which  is  variously  designated  as 
the  ' dry- wall'  or  the  l rock- wall'  and  again  simply  as  a 
'  filling  system/ 

Copper  occurs  in  the  native  state  in  the  Lake  Superior 
copper  region,  being  found  in  both  sedimentary  and  inter- 
stratified  igneous  rocks.  The  copper  constitutes  a  cement 
which  binds  together  and  replaces  the  pebbles  and  boulders 
of  porphyry  conglomerate,  or  fills  the  amygdules  especially 
in  the  upper  portions  of  the  interbedded  massive  rocks. 
In  the  Quincy,  Franklin  and  Atlantic  mines  the  lodes 
are  amygdaloidal,  i.e.,  are  strongly  altered  diabase,  parts 
of  which  are  known  as  ash-beds.  (See  Fig.  23.) 

Stations  are  established  in  the  shafts  every  100  to  125 
feet  along  the  lodes  from  which  levels  are  driven  8  feet  high 
and  the  width  of  the  lode  wide.  The  level  drifts  are  en- 
larged by  cutting-out  stoping,  and  from  the  rock  broken 
down  the  larger  pieces  of  waste  are  employed  in  building 
the  pack  or  so-called  dry-walls  or  rock-walls,  which  are 
8  feet  high.  On  these  walls  timbers  are  placed  which  reach 
from  wall  to  wall,  upon  which  in  turn  is  laid  a  lagging  of 


86 


ORE  MINING   METHODS 


<u 

bo 

c 


MINING  IN  NARROW  VEINS  AND  BEDDED  DEPOSITS     87 

plank  or  poles.  The  timbers  are  called  'wall-pieces'  and 
vary  in  size  from  18  to  24  inches,  being  14  feet  long.  As 
the  work  of  stoping  proceeds  the  waste  rock  sorted  out  is 
stowed  between  the  pack-walls  and  the  foot-  and  hanging- 
walls  until  these  spaces  are  full  and  is  then  thrown  upon  the 
lagging  covering  the  walled  passage.  Mill-holes  are  begun 
on  the  foot-wall  side  of  the  passage  and  are  built  up  as  the 
stope  increases  in  height.  (See  Fig.  23.)  The  mill-holes 
are  round,  5  feet  in  diameter,  and  when  completed  are  about 
50  feet  deep.  Owing  to  the  steepness  and  width  of  the  lodes 
it  is  necessary  to  mount  the  drills  employed  in  cutting-out 
stoping  between  the  working  face  and  the  broken  ore  and 
rock  below.  Pickers  and  trammers  work  at  the  rear  of 
the  bank  of  broken  rock,  sorting  out  the  pay-rock  and  stow- 
ing the  waste  in  the  stope,  thus  leveling  the  rock  as  it  is 
broken  down  in  advance.  From  25  to  45  per  cent  of  the 
lode-rock  is  waste  and  is  available  for  filling;  however,  if 
there  is  not  a  sufficient  quantity  to  fill  the  stopes,  the  foot- 
wall  may  be  broken  down  to  furnish  more. 

Cutting-out  stoping  is  continued  up  to  within  about 
20  feet  of  the  level  above,  when  it  is  stopped,  thus  leaving 
an  arch  pillar,  which  is  broken  at  more  or  less  regular  inter- 
vals by  openings  or  'break-throughs.' 

At  the  Trimountain  Mine,  especially  owing  to  the  irregu- 
larity of  the  foot- wall  and  fairly  uniform  hanging- wall,  it  is 
considered  advisable  to  carry  all  development  work  close  to 
the  latter. 

As  the  work  of  extracting  the  ore  proceeds  from  above 
downward,  an  upper  stope  is  first  worked  out,  and  when  there 


88  ORE  MINING  METHODS 

is  no  further  need  of  support  or  protection  of  the  level  the 
filling  is  drawn  off  into  the  next  lower  stope,  where  it  serves 
a  useful  purpose  in  assisting  in  stoping  out  the  arch  pillars 
by  providing  a  support  for  the  miners  in  drilling.  The 
filling  is  drawn  off  by  making  openings  in  the  pack-walls 
of  the  filled  stopes  at  points  directly  over  break-throughs  in 
the  arch  pillars  of  the  stopes  to  be  filled.  The  stopes  are 
then  allowed  to  fill  as  full  as  the  size  of  the  break-throughs 
will  permit.  Drills  are  then  mounted  under  the  ends  of 
the  pillars,  adjacent  to  and  on  the  inclined  surface  of  the 
fills.  A  portion  of  the  pillars  about  10  feet  in  width  and 
from  15  to  20  feet  in  length  is  then  removed  as  in  cutting- 
out  stoping.  The  drills  are  then  reversed  and  holes  are 
drilled  which  when  charged  and  fired  will  break  down  the 
ends  of  the  pillars,  thus  enlarging  the  openings  through 
which  the  filling  flows.  By  these  two  successive  operations 
the  arch  pillars  are  gradually  removed,  footing  for  the 
miners  being  provided  by  the  movement  of  the  filling  from 
above,  thus  maintaining  the  same  relative  position  with 
respect  to  the  pillars.  The  rock  as  broken  from  the  pillars 
falls  upon  the  surface  of  the  filling  and  is  carried  to  the  pick- 
ers below  by  its  downward  and  lateral  movement.  A  num- 
ber of  break-throughs  may  be  opened  in  a  similar  manner 
in  the  same  stope,  thus  permitting  rapid  removal  of  the  arch 
pillars  and  the  filling  of  the  stopes.  Picking  of  pay-rock  and 
spreading  of  waste  are  carried  on  as  in  cutting-out  stoping. 
The  method  is  applicable  to  moderately  wide  and  steeply 
dipping  lodes  from  which  considerable  waste  rock  can  be 
obtained  by  sorting  and  if  necessary  from  special  excava- 


MINING  IN  NARROW  VEINS  AND  BEDDED  DEPOSITS      89 

tions.     The  ore  and  walls  should  be  fairly  strong  and  firm,  as 
they  must  stand  temporarily  often  for  considerable  distances 
without  support. 
The  advantages  of  the  filling  method  described  above  are : 

1.  Little  timber  is  required. 

2.  The  complete  extraction  of  ore  in  the  lode. 

3.  All  waste  rock  is  stowed  in  the  mine  with  little  han- 
dling. 

4.  A  fairly  clean  product  is  sent  to  the  surface. 

5.  Ease  of  stoping  and  reduced  cost  of  mining. 

6.  The  repeated  use  of  filling  for  support  of  workings. 

7.  Placing  of  levels  a  considerable  distance  apart. 
The  disadvantages  of  the  method  are: 

1.  Applicable  to  highly  inclined  lodes. 

2.  Cost  of  building  pack- walls. 

3.  Considerable  handling  of  ore  in  stopes. 

4.  Collapse  of  upper  levels  on  withdrawal  of  filling  and 
danger  of  a  crush  starting  and  extending  to  lower  levels. 

5.  Loss  of  ore  by  mixing  with  waste  in  cutting-out  arch 
pillars. 

MINING  BEDDED  DEPOSITS  BY  CAVING 

The  sub-drift  system  of  mining  has  been  successfully 
employed  in  the  Mercur  and  Golden  Gate  mines  of  Mercur, 
Utah.  The  ores  are  oxidized  and  base,  i.  Mercur  and  Golden 

Gate  Mines,  Mer- 

carrying  gold  and  occur  in  a  limestone         cur,  Utah. 

J  2.  Gold  Ore. 

formation.     The  dip  of  the  ledges  ranges  3.  Bedded  deposit. 

4.   15  to  20  ft.  thick 

from  a  few  degrees  up  to  25  ,  necessitat-  and  up. 

ing  the  use  of  inclines  to   develop  the  ore-bodies,  which 


ORE  MINING  METHODS 


o 
Q 


oo 


are  often  driven  next  to  the  roof  or  in  the  upper  part  of 
the  mineralized  portion  of  the  ledge.  When  driven  at  the 
bottom  of  the  ore-body,  as  shown  in  Fig.  24,  there  is  more 
danger  of  the  passage  being  destroyed  by  the  caving  of 
ground  above. 


MINING  IN  NARROW  VEINS  AND   BEDDED   DEPOSITS     91 

When  the  ledge  is  15  to  20  feet  thick,  the  part  above  the 
line  AB  may  represent  the  ledge  worked,  the  incline  being 
shown  by  the  dotted  lines.  With  ledges  of  greater  thick- 
ness, often  reaching  100  feet,  the  whole  section,  as  shown, 
would  represent  the  conditions,  the  incline  being  at  the 
bottom  of  the  ledge.  The  system  of  working  thin  ledges 
is  quite  simple  and  can  be  described  to  advantage  prior 
to  taking  up  the  more  complicated  method  of  working  the 
thicker  ledges. 

An  incline  having  been  run  along  the  line  AB,  the  assumed 
floor  of  the  deposit,  ' sub-drifts'  are  driven  from  15  to 
25  feet  apart  horizontally  and  to  the  limit  of  the  workable 
deposit.  (See  Fig.  24.)  Stoping  is  then  begun  on  the  sides 
of  the  'sub'  No.  i,  supporting  posts  or  stulls  in  the  higher 
dips  being  placed  as  the  stope  widens.  When  the  stope 
faces  of  subs  Nos.  i  and  2  have  been  connected  by  break- 
ing through,  the  pillar  between  them  and  that  portion 
between  sub  No.  i  and  the  caved  ground  are  drawn  back 
by  breast  stoping  or  '  side-swiping '  and  the  ore  in  the  roof 
is  caved  by  knocking  out  posts  and  blasting  the  back.  The 
drifts  furnish  protection  for  the  men  when  caving  is  under 
way.  In  a  similar  manner  the  pillars  between  subs  Nos.  2 
and  3  and  3  and  4,  and  so  on,  as  rapidly  as  the  subs  are 
driven,  may  be  drawn  and  the  roof  caved.  Each  retreat- 
ing pillar  face  is  kept  from  12  to  20  feet  in  advance  of  the 
adjacent  one  down  the  slope,  thus  maintaining  conditions 
best  suitable  to  pillar-drawing  as  determined  by  experience 
in  these  mines  and  similar  work  in  coal  mining.  Under  the 
most  favorable  conditions  the  removal  of  drift  sets  and  posts 


92  ORE  MINING  METHODS 

is  all  that  is  necessary  to  start  the  back  caving.  The  miner 
then  shovels  the  ore  into  cars  and  trams  it  to  chutes  pro- 
vided at  intervals  of  about  50  feet.  (See  Fig.  25.) 

When  waste  begins  to  come  and  mix  with  the  ore  it  is 
evident  that  the  roof  formation  is  down,  and  the  miner 
prepares  for  another  cave  by  taking  out  the  supporting 
posts  next  to  the  face.  Under  no  condition  should  a  lower 
pillar  be  allowed  to  retreat  faster  than  an  upper,  as  a 
cave  would  be  almost  sure  to  take  place  in  the  upper  pillar, 
loosing  ore  and  endangering  the  miners  working  in  the 
sub  above. 

In  thick  deposits  the  same  method  of  procedure  is  fol- 
lowed but  is  applied  to  a  series  of  inclined  benches  which 
are  about  15  feet  thick,  the  respective  series  of  subs  being 
connected  by  cross-cuts.  The  upper  portion  of  the  deposit 
is  carried  considerably  in  advance  of  the  lowermost  bench, 
each  bench  being  advanced  in  a  manner  and  amount  similar 
to  the  retreating  pillar  faces  in  the  separate  benches  as 
previously  described.  (See  Fig.  25.) 

Under  certain  conditions  of  deposit  and  roof  the  whole 
deposit  throughout  the  series  of  sub-levels  may  be  caved 
at  one  and  the  same  operation  by  beginning  at  the  top  and 
starting  a  cave  in  each  sub.  The  whole  vein  can  in  this 
manner  be  caved  and  drawn  off  without  difficulty,  but  the 
work  has  to  be  conducted  with  great  care. 

The  caving  system  as  employed  in  the  Mercur  mines  is 
suited  to  both  thick  and  thin  deposits  inclined  at  moderate 
and  low  inclinations.  It  is  especially  applicable  to  deposits 
of  uniform  thickness  where  both  ore  and  roof  or  hanging- 


MINING  IN  NARROW  VEINS  AND   BEDDED   DEPOSITS      93 


94  ORE  MINING  METHODS 

wall  are  sufficiently  weak  to  break  and  cave  readily.     It  is 
equally  applicable  to  both  high-  and  low-grade  deposits. 
The  advantages  of  the  system  are: 

1.  It  has  a  wide  range  of  application  as  to  thickness  of 
deposit. 

2.  A  large  percentage  of  extraction  is  possible. 

3.  A  small  amount  of  timber  and  powder  is  used. 

4.  Safety  of  men. 

The  disadvantages  of  the  system  are: 

1.  It  is  limited  to  deposits  of  moderate  inclinations. 

2.  It  is  difficult  to  keep  different  grades  of  ore  separate. 

3.  There  is  always  danger  of  loss  of  ore  from  caving 
ground. 

4.  It  cannot  be  employed  to  advantage  where  the  top 
formations  are  hard  and  firm  and  do  not  cave  readily. 


CHAPTER  IV 

METHODS    OF   MINING    IN    WIDE    VEINS 
AND    MASSES 

INTRODUCTION 

THE  methods  of  mining  employed  in  large  deposits,  as 
wide  veins  and  masses,  often  vary  but  little  from  those  used 
in  similar  but  smaller-sized  deposits.  Mining  with  square- 
sets  as  well  as  the  filling  and  caving  methods  are  commonly 
employed  in  both  large  and  small  deposits  and  usually  with 
equal  facility,  with  the  possible  exception  of  the  first  named, 
or  square-setting,  which  has  its  limitations  and  probably 
has  its  widest  range  of  usefulness  in  the  smaller  and  medium 
sized  deposits.  Square-set  mining  is  now  being  rapidly 
replaced  by  the  filling  and  caving  methods,  and  its  use, 
largely  for  economic  reasons,  will  be  relegated  to  the  work- 
ing of  certain  deposits  of  special  shape  and  occurrence  and 
advantageously  located  with  respect  to  an  available  supply 
of  suitable  timber  or  transportation  facilities. 

The  methods  of  mining  described  and  discussed  in  this 
chapter  may  be  grouped  into  a  number  of  classes,  which 
are  arranged  in  the  following  order:  shrinkage  stoping 
methods  of  mining;  square-set  methods  of  mining;  filling 
methods;  and  caving  methods. 

The  width  of  veins  considered  in  this  connection  ranges 
from  35  to  40  feet  as  a  minimum  to  several  hundred  feet, 
while  massive  deposits  of  all  sizes  are  included. 

95 


96 


ORE  MINING  METHODS 


MINING  IN  WIDE  VEINS  AND  MASSES  97 

SHRINKAGE  STOPING  METHODS  OF  MINING 
The  method  employed  in  the  Gold  Prince  Mine  located 
at  Animas  Forks,  Colorado,  illustrates  the  application  of 
overhand  stoping  to  a  very  wide  lode  of  i.  Gold  Prince  Mine, 

,  -,  ^  .     f  ,  ,  Animas  Forks, 

low-grade  ore.     The  ore  is  free  gold  and        Colo. 

.,  ,  ,  .   A     ,    2.  Gold  and  Silver. 

silver  in  a  gangue  of  quartz  and  associated  3.  vein. 

.,,  .  ,    ,.  ,         xl_  ,  .4.  Width  30  to  130 

with  various  sulphides,  the  value  ranging        ft. 
between  $8  and  $12  per  ton.     The  lode  varies  in  width 
from  30  to  130  feet,  averaging  probably  50  to  60  feet. 
The  wall-rock  is  andesite,  usually  very  tough  and  strong. 

The  lode  is  developed  by  a  tunnel  which  cuts  it,  a  main 
drift  being  driven  in  the  lode  midway  between  the  walls. 
(See  Fig.  26.)  Cross-cuts  are  driven  across  the  lode  at 
intervals  of  200  to  300  feet  along  the  line  of  the  main  drift, 
which  determine  the  width  of  the  lode  also  the  length  of 
the  stopes.  Pillars  18  feet  in  width  are  left  between  stopes 
through  which  man-ways  are  cut  connecting  the  levels. 
Openings  are  made  at  frequent  intervals  in  these  pillars  on 
either  side  of  the  man-ways  in  order  to  provide  entrance  to 
the  stopes.  From  the  backs  of  the  levels,  chute-raises  are 
put  up  every  30  feet  and  extend  some  10  feet  vertically, 
beyond  which  point  four  inclined  raises  are  driven,  two 
extending  along  the  line  of  the  lode,  the  other  two  running 
transversely  with  it  until  the  walls  are  encountered.  Stop- 
ing  is  begun  from  these  raises  and  carried  on  both  laterally 
and  vertically  until  inverted  conical-shaped  openings  have 
been  formed,  from  the  lowermost  points  of  which  the  chute- 
raises  extend  to  the  levels  below,  being  provided  with  load- 
ing chutes  through  which  the  cars  are  filled.  (See  Fig.  27.) 


98  ORE  MINING  METHODS 

As  the  ore  is  strong  and  solid  it  stands  well  without  support, 
and  the  thick  back  of  ore  in  the  form  of  stump-pillars  insures 
against  danger  from  caving  ground  in  the  stopes.  Owing 
to  the  great  width  and  length  of  stopes,  the  work  of  stoping 
can  be  carried  on  very  rapidly  and  at  the  same  time  the 
boulders  can  be  reduced  to  such  a  size  as  to  readily  pass 
through  the  chutes.  It  is  only  necessary  to  draw  off  about 
30  per  cent  of  the  broken  ore  to  provide  room  for  the  miners 
to  work  at  the  face,  the  remainder  being  left  in  the  stopes  if 
desired  as  a  reserve.  The  ore  is  hard  and  dry  and  does  not, 
therefore,  pack  in  the  stopes  nor  break  up  while  being  with- 
drawn therefrom.  A  stope  having  been  worked  up  to  the 
level  above,  and  the  ore  drawn  off,  an  attempt  may  be 
made  to  cut  out  the  stump-pillars,  which  can  be  done  by 
underhand  stoping  to  a  certain  point,  after  which  there  is 
danger  of  the  stope  collapsing,  although  probably  the  greater 
part  of  the  ore  can  be  secured. 

The  method  of  mining  employed  in  the  Gold  Prince  Mine 
resembles  in  many  respects  the  practice  in  the  Alaska- 
Treadwell  mines,  although  owing  to  the  smaller  size  of 
deposit  it  is  on  a  very  much  smaller  scale.  The  method  is 
applicable  to  wide  deposits  of  low-grade  ore,  which  is  both 
hard  and  strong,  standing  without  support,  and  with  strong 
wall-rock. 

The  deposit  should  also  stand  nearly  vertical  in  order  that 
the  method  may  have  the  widest  range  of  application. 

The  advantages  of  the  method  are : 

1.  No  timber  or  other  support  is  required. 

2.  The  output  is  large. 


MINING  IN  WIDE  VEINS  AND   MASSES 


99 


~]~1VM  9NISNVH 


loo  ORE  MINING  METHODS 

3.  The  cost  of  mining  is  low. 

4.  A  reserve  of  broken  ore  is  available  at  any  time. 

5.  Handling  of  ore  is  reduced  to  a  minimum. 

6.  Ventilation  is  good. 

7.  The  workings  are  easy  of  access. 

8.  Little  development  work  is  necessary. 
The  disadvantages  of  the  method  are: 

1.  Limited  to  large  highly  inclined  deposits. 

2.  There  is  no  opportunity  to  sort  or  stow  waste  rock. 

3.  Considerable  loss  of  ore  in  pillars. 

The  mining  of  the  immense  deposits  of  low-grade  gold  ores 
of  the  Alaska-Treadwell  mines,  Alaska,  has  been  from 
i.  Alaska-Treadwell  tne  beginning  of  their  exploitation  the  sub- 
,  Alaska!  Ject  of  mucn  study  and  experimentation 


2.  Gold  Ore.  until  a  method  has  been  developed  which 

3.  Massive  deposit 

standing  vertically  seems  to  be  eminently  suited  to  the  exist- 

or  nearly  so. 

4.  Thickness  several  ing  Conditions. 

hundred  feet.  ^  ,.      .,        .     ,        n          , 

The  ore  occurs  in  dionte,  is  hard  and 
firm,  and  stands  well  both  in  pillars  and  stope-backs.  The 
ore-bodies  are  lenticular  in  shape  and  dip  from  50  to  65°, 
the  foot-wall  being  schist  and  moderately  soft,  while  the 
hanging-wall  is  greenstone  or  gabbro,  and  is  hard. 

The  method  of  developing  the  ore-bodies  consists  in  sink- 
ing a  shaft  in  the  foot-wall  from  which  levels  are  driven  to 
and  through  the  deposit.  At  the  intersection  of  the  levels 
with  the  foot-  wall,  drifts  7  by  10  feet  in  section  are  run  par- 
tially in  the  foot-wall  and  partially  in  the  deposit.  The 
positions  of  the  pillars  having  been  decided  upon,  those  of 


MINING  IN  WIDE  VEINS  AND   MASSES  101 

the  various  levels  being  located  vertically  one  above  the 
other,  main  raises  6  by  7  feet  in  section  are  put  up  at  in- 
tervals of  about  200  feet,  which  places  a  raise  in  alternate 
pillars.  These  raises  make  connection  with  the  various 
levels,  which  are  now  driven  200  feet  apart.  The  distance 
between  levels  has  been  increased  from  no  feet,  the  original 
distance,  to  the  height  of  200  feet  now  employed.  Midway 
between  the  proposed  centers  of  pillars  cross-cuts  are  driven 
across  the  deposit  paralleling  the  pillars.  At  intervals  of 
60  feet  along  the  cross-cuts,  drifts  are  run  normal  to  them 
and  parallel  with  the  longer  dimension  of  the  ore-body. 
Other  raises  are  put  up  in  pillars  along  the  line  of  the  drift 
next  to  the  hanging-wall.  The  object  of  these  raises  is  to 
ventilate  the  various  levels.  Other  raises  are  put  up  at 
25-foot  intervals  along  both  drifts  and  cross-cuts  and  are 
termed  'chute-raises/  At  a  height  of  18  to  20  feet  and 
thereafter  at  intervals  of  30  feet '  blind  drifts '  or  i  sub-drifts ' 
are  driven  on  either  side  of  the  main  raises  and  extend  at 
right  angles  to  the  pillars.  (See  Fig.  29.) 

The  first  sub-drift  is  driven  as  a  drift-stope  across  the 
body  of  ore  lying  between  pillars,  and  as  it  is  extended 
breaks  into  the  tops  of  the  chute-raises.  The  drift-stope 
is  8  feet  in  height,  and  when  widened  out  on  either  side 
of  the  line  of  chute-raises  it  forms  the  beginning  of  the 
stope  or  the  cutting-out  floor.  The  tops  of  the  chute- 
raises  are  enlarged  into  funnel-shaped  openings  in  order  to 
more  readily  collect  the  ore  broken  down  from  above. 
The  chute-raises  should  be  kept  full  to  protect  them  from 
falling  ore. 


IO2 


ORE  MINING  METHODS 


MINING   IN  WIDE  VEINS  AND  MASSES  103 

After  the  drift-stope  has  been  extended  from  one  pillar 
to  another  and  the  '  stope-floor '  established  the  work  of 
opening  the  whole  stope  is  begun.  Drills  are  set  up  in  the 
center  of  the  stope-floor  on  tripods  and  a  drift-stope  is  run 
longitudinally  the  full  length  of  the  stope.  This  drift-stope 
is  then  enlarged  laterally  by  breast  work  until  the  pillars 
have  been  reached.  Considerable  care  is  taken  in  forming 
the  back  of  the  stope  into  an  arch  with  sufficient  curvature 
to  stand  readily.  As  previously  pointed  out,  the  character 
of  the  ore  is  such  that  it  stands  well  in  low  arches  of  wide 
span,  thus  permitting  wide  stopes  to  be  maintained.  The 
larger  fragments  of  ore  resulting  from  blasting  in  the  stopes 
must  be  reduced  by  sledge-hammers  and  small  charges  of 
powder  to  a  size  to  pass  the  chutes.  The  latter  operation 
is  known  as  t  bulldozing.'  It  has  been  found  that  the 
broken  ore  requires  one- third  more  space  than  the  solid  ore, 
consequently  one-third  must  be  removed  to  provide  room 
for  the  miners  at  the  working  face.  (See  Fig.  29.) 

As  the  work  of  cutting-out  the  back  of  the  stope  continues 
the  various  sub-drifts  are  broken  into,  thus  maintaining 
access  to  the  stopes  and  providing  a  passage  for  air  currents. 
Ultimately  the  stope  breaks  into  the  level  above,  but  instead 
of  carrying  it  up  the  full  width  it  is  arched,  only  the  crown 
of  the  arch  being  broken  through.  A  ledge  is  then  left 
in  the  stope-floor  above,  which  is  supported  by  the  flaring 
tops  of  the  pillars  below.  These  ledges  are  termed  '  sheet- 
pillars  '  and  are  in  reality  pentices,  as  their  primary  object 
is  to  serve  as  a  protection  to  the  men  employed  in  the  stope 
beneath. 


104  ORE  MINING  METHODS 

The  pillars  are  approximately  100  feet  center  to  center, 
the  length  varying  with  width  of  ore-body  and  may  be  300 
feet.  The  width  of  the  pillars  varies  from  18  to  25  feet  and 
they  are  often  considerably  wider  especially  with  the  height 
of  stopes  now  employed.  The  height  of  the  stope  is  about 
185  feet,  or  twice  the  width,  the  increased  height  being  con- 
sidered more  economical,  as  fewer  levels  have  to  be  formed. 

The  method  of  mining  employed  in  the  Alaska-Treadwell 
mines  is  applicable  to  very  large  deposits  of  low-grade  hard 
and  firm  ore,  also  to  deposits  standing  at  high  inclinations. 

The  advantages  of  the  method  are : 

1.  Levels  can  be  placed  far  apart. 

2.  Practically  no  timber  is  used. 

3.  Large  output  for  number  of  men  employed. 

4.  The  cost  of  extraction  of  ore  is  small. 

5.  Handling  ore  reduced  to  a  minimum. 

6.  Little  danger  from  accidents. 

The  disadvantages  of  the  method  are: 

1.  Is  applicable  only  to  large  deposits  of  high  dips. 

2.  .The  stopes  must  be  carried  up  vertically. 

3.  The  amount  of  development  work  required  for  each 
level  is  large. 

4.  System  of  ventilation  rather  complicated. 

5.  Loss  of  ore  in  pillars  rather  large,  especially  if  a  regular 
system  is  followed  in  laying  out  workings. 

SQUARE-SET  METHODS  OF  MINING 

Timbering  by  square-sets,  in  which  the  members  of  the 
sets  are  unsawed  round  timbers,  is  common  practice  in 


MINING  IN  WIDE  VEINS  AND  MASSES 


=5 
I 

I 


I 


I 


io6  ORE  MINING  METHODS 

many  parts   of   the   country.     In   Fig.  30  is   shown  the 

system  of  square-setting  with  round  timbers  as  employed 

,  in  the   mines    of    Rossland,  British   Co- 

1.  Mines  at  Rossland, 

B-  c-  lumbia.     The    ore    deposits    often    have 

2.  Gold  and  Copper 

Ore.  widths  ranging  up  to  100  feet  and  dip  at 

3.  Veins.  ,          .      ,  o        -r»    ,1  i 

4.  Maximum  width   an  angle  of  about   7°  •      B°th  ore  and 

ft*  wall-rock  are  very  hard,  the  former  being 

badly  fractured  and  fissured  wall-rock,  which  is  cemented 
together  with  auriferous  sulphides.  The  conditions  existing 
in  these  deposits  are  decidedly  favorable  for  the  employ- 
ment of  square-sets. 

Stoping  is  done  by  the  overhand  system,  the  work  being 
started  from  a  raise  or  winze  and  proceeding  in  both  direc- 
tions. The  work  is  carried  on  in  floors,  each  floor  being 
somewhat  over  a  set  high  and  terminating  in  a  back-stope, 
i.e.,  if  there  are  four  back-stopes  there  are  five  floors  includ- 
ing the  drift-stope.  The  square-sets  in  the  stopes  assume  a 
stepped  formation,  dropping  down  set  by  set  in  both  direc- 
tions from  the  raise.  The  timbers  composing  the  sets 
range  in  diameter  from  12  to  20  inches,  averaging  about 
1  8  inches,  and  are  partially  seasoned  before  being  used  in  the 
mines. 

Square-sets  have  been  extensively  employed  in  mining 
the  iron  ores  of  the  Lake  Superior  region,  but  have  been 

1.  Queen  Mine,         largely  superseded  in  the  massive  deposits 

Negaunee,  Mich.  .  -,  ^ 

2.  iron  Ore.  ^Y  tne  caving  methods,  such  as  the  top 


3.  Massive  Deposit.  s\[c^  SUD-drift  and  modifications  of  these 

4.  Large  lens-shaped 

body.  with  the  milling  method. 

A  special  method  involving  both  the  use  of  square-sets 


MINING  IN  WIDE  VEINS  AND   MASSES 


107 


Fig.  30.  —  Square-Sets  composed  of  Round  Timbers. 

and  caving  has  been  employed  in  the  various  districts  and 
is  at  present  in  successful  operation  at  the  Queen  Mine, 
Negaunee,  Michigan.  The  ore  body  here  is  large  and  lens- 
shaped,  being  quite  regular.  It  has  a  dip  of  38°  to  the 
north  and  pitches  45°  to  the  west.  Owing  to  its  size  and 
regularity  it  is  especially  suited  to  systematic  and  large- 
scale  operations.  (See  Fig.  31.) 

The  deposit  is  opened  by  vertical  shafts,  and  on  the  levels 
are  well-planned  systems  of  haulage-ways  through  which 


108  ORE  MINING  METHODS 

the  empty  and  loaded  trains  of  cars  can  travel  without 
interference.  In  the  deposit  a  number  of  stope-faces  are 
carried  three  sets  wide,  usually  parallel  with  the  major  axis 
of  the  ore-body,  and  at  intervals  of  40  feet  (five  sets)  apart 
other  similar  stopes  are  then  run,  cross-cutting  the  former 
and  at  equal  intervals.  The  deposit  is  then  broken  up  into 
rooms  (stopes)  and  pillars;  the  former  25  feet  wide  and  by 
continued  stoping  carried  about  50  feet  high,  the  latter 
40  feet  square  and  of  equal  height  with  the  stopes.  The 
stopes  are  carefully  supported  by  square-sets,  those  of  the 
upper  level  extending  to  caved  ground,  if  mining  has  pre- 
viously been  carried  on  above,  if  not  to  barren  ground. 

The  next  operation  is  the  drawing  or  robbing  of  the  pillars, 
following  which  caving  begins.  A  pillar  is  removed  by 
driving  two  drifts  through  the  base,  i.e.,  on  the  level  of  the 
stope-floor,  cross-cutting  it  into  four  equal  parts.  At  the 
point  of  intersection  of  the  drifts,  or  the  center  of  the  pillar, 
an  8  by  8-foot  raise  is  put  up  through  the  pillar,  both  drifts 
and  raise  being  timbered  with  sets.  The  backs  of  the  drifts 
are  next  stoped  out  to  the  height  of  the  centrally  located 
raise,  thus  completely  subdividing  the  pillar  into  four  equal 
parts.  Stoping  is  then  begun  at  the  top  of  the  raise,  and  the 
upper  portion  of  the  new  pillars  formed  is  removed  to  the 
depth  of  one  set.  A  cap  of  double  length  is  placed  next  to 
the  roof  and  lagging  carefully  put  in  place  above  it.  The 
work  of  cutting  away  the  pillar  is  then  resumed,  and  other 
double-length  caps  are  placed  as  rapidly  as  possible.  On 
placing  the  second  cap  it  is  usual  to  reenforce  the  first  or 
roof  cap  by  two  timbers  set  in  A-form.  The  ore  broken  from 


MINING  IN  WIDE  VEINS  AND  MASSES  log 


VERTICAL  SECTION 


oTl 


PLAN 


Fig.  31.  — Square-set  Mining  in  Massive  Deposit. 


HO  ORE  MINING   METHODS 

the  pillars  falls  upon  lagging  placed  at  the  lower  side  sets, 
from  which  it  is  run  or  shoveled  into  cars.  That  part  of 
the  ore  obtained  from  pillar-drawing  is  the  easiest  got  in 
all  of  the  mining  operations. 

The  ore  having  been  all  mined  out,  the  tracks  are  removed 
and  the  timbers  are  broken  down  by  blasting  every  second 
leg  of  the  sets,  which  starts  the  cave.  When  all  movement 
has  ceased,  the  next  level  may  be  worked  out  in  a  similar 
manner,  but  so  far  the  method  has  been  confined  to  work- 
ing out  the  upper  portion  of  deposits,  subsequent  work 
being  done  by  strictly  caving  methods. 

This  combination  method  of  square-setting  and  caving 
is  applicable  to  massive  deposits  of  hard  ore  which  stand 
well  and  to  deposits  that  occur  close  to  the  surface  and  of 
large  lateral  extent. 

The  advantages  of  the  method  are: 

1.  A  large  output  is  possible. 

2.  The  cost  of  mining  is  low. 

3.  There  is  little  danger  from  falls. 

4.  Opportunity  is  given  for  the  sorting  of  ore  if  desirable. 
The  disadvantages  of  the  method  are: 

1.  It  is  of  limited  application,  being  seldom  used  in  more 
than  one  floor. 

2.  A  large  amount  of  timber  is  required. 

3.  Loss  of  timber  is  great. 

FILLING  METHODS 

The  economic  working  of  the  large  ore-bodies  of  the  lode 
of  Broken  Hill,  New  South  Wales,  Australia,  has  necessi- 


MINING   IN  WIDE   VEINS  AND   MASSES 


III 


tated  radical  changes  in  methods  of  mining  .until  at  pres- 
ent fully  three  different  methods  are  in  use  in  various 
parts  of  the  lode.  The  ore  is  lead-silver,  1.  Broken  Hill  Mines, 
although  other  minerals  of  economic  value  2.  Lead  and  Silver 

Ore. 

are  obtained.     The  lode  ranges  in  width  3.  Vein. 

4.   Width   25   to 

from  25  to  370  feet,  averaging  probably        370  ft. 

70  or  80  feet,  and  stands  nearly  vertically.    The  ore  varies 


112  ORE  MINING  METHODS 

from  very  hard  to  very  friable,  the  wall-rock  also  varying 
somewhat  in  hardness  and  strength.  These  conditions  are 
also  responsible  for  changes  in  methods,  as  well  as  for  the 
employment  of  various  methods  in  the  different  mines  of 
the  district.  The  tendency  has  been  to  employ  methods 
in  which  the  quantity  of  timber  used  is  small  and  is  be- 
coming of  less  importance  as  a  factor  in  the  extraction 
of  ore. 

There  are  three  methods  in  use  in  these  mines  which  may 
be  employed  in  illustrating  the  gradual  change  in  working, 
showing  the  evolution  from  one  to  another  and  therefore 
having  points  of  resemblance.  These  methods  are,  in  the 
order  of  their  development,  square-setting,  the  'open-stope,' 
and  the  i  pillar-and-stope.' 

The  application  of  square-set  timbering  as  a,  means  of 
support  and  a  convenience  in  mining  and  handling  ore  in 
the  stopes  is  well  illustrated  by  the  practice  in  this  district. 
This  system  is  employed  in  ground  that  is  not  sufficiently 
strong  to  stand  by  itself,  as  in  the  friable  sulphides.  The 
all-square-set  system  is  usually  employed  in  the  narrower 
portions  of  the  lode,  although  it  has  been  used  in  the  large 
ore-bodies.  The  sets  are  usually  7  by  5  by  6  feet,  i.e.,  posts 
7  feet,  girts  5  feet,  and  caps  6  feet  long,  although  in  the  Cen- 
tral and  Proprietary  mines  the  sets  are  8  by  6  by  6  feet. 
When  the  face  is  hard  and  solid  it  may  stand  with  only  an 
occasional  supporting  prop  between  it  and  the  square-sets, 
but  when  friable  the  sets  may  have  to  be  kept  close  to  the 
face.  The  disadvantage  of  carrying  the  timbering  close  to 
the  face  is  that  blasts  are  liable  to  injure  or  knock  down 


MINING  IN  WIDE  VEINS  AND   MASSES  113 

the  sets,  which  is  expensive  from  the  standpoint  of  loss  of 
timber  and  delay,  and  may  also  result  in  falls  of  rock.  (See 
Figs.  32  and  33.) 

The  method  of  placing  lagging  for  the  miners  to  stand 
upon  while  working  at  the  face  is  shown,  also  the  arrange- 
ment of  chutes  and  pockets  for  handling  and  holding  ore 
preparatory  to  loading  it  into  cars. 

The  open-stope  method  of  mining  as  employed  in  the 
Broken  Hill  mines  is  in  successful  operation  in  portions  of 
the  lode  that  average  70  to  80  feet  in  width  and  often  reach- 
ing a  width  of  200  feet.  Where  used  the  walls  are  firm  and 
the  ore  is  solid,  standing  fairly  well  by  itself.  Owing  to  the 
great  width  of  the  lode,  a  portion,  usually  somewhat  less  than 
one-half,  is  left  as  a  pillar,  although  it  is  planned  to  ulti- 
mately mine  all  the  ore.  (See  Fig.  34.) 

The  lode  is  developed  by  vertical  shafts  sunk  in  the  foot- 
wall  from  which  levels  are  driven  some  20  to  30  feet  from  and 
paralleling  the  lode.  From  the  foot-wall  levels,  cross-cuts 
are  made  at  intervals  of  80  to  100  feet  to  and  through 
the  lode  until  the  hanging- wall  is  reached,  when  they  are 
opened  up  on  either  side.  Connecting  the  cross-cuts  and 
through  the  center  of  the  lode  is  a  drift,  which  serves  as 
the  main  haulage-way.  Combined  ore  chutes  and  man- 
ways  are  placed  every  30  feet  along  the  haulage-way,  being 
timbered  passages  built  up  as  the  stope  increases  in  height. 
The  cross-cuts  are  timbered  with  square-sets  as  formed,  and 
are  extended  laterally  until  they  run  together,  if  that  is 
found  desirable,  thus  forming  a  long  continuous  stope. 
The  cross-cuts  and  afterward  the  stopes  are  carried  n  to  12 


ORE  MINING  METHODS 


feet  high,  which  is  done  in  two  operations:  the  lower  5  or  6 
feet  by  drifting  and  breast  stoping,  the  upper  6  feet  by 


mounting  the  drills  on  a  crib-work  of  timbers.  Beginning 
with  the  foot-wall  side  of  the  lode  square-sets  are  placed,  but 
kept  far  enough  back  from  the  face  to  prevent  injury  by 
blasting.  As  an  additional  support  cribs  are  built  in  ad- 


MINING  IN  WIDE  VEINS  AND   MASSES  115 

vance  of  the  sets,  thus  insuring  the  support  of  the  back 
under  ordinary  conditions.  A  method  of  extending  certain 
members  of  the  crib  that  come  next  to  the  back  as  cantile- 
vers to  support  bad  ground,  which  is  held  in  place  by  wedges, 
is  an  important  factor  in  the  system  of  control  of  back. 
On  completing  the  level  or  sill-floor  and  having  filled  the 
stope  to  within  a  few  feet  of  the  back,  the  work  of  removing 
another  horizontal  slice  is  begun,  the  cutting-out  being 
carried  on  as  before,  except  that  no  sets  are  used  above  the 
sill-floor,  cribs  being  the  only  form  of  timber  support  em- 
ployed. The  waste-filling  is  run  into  the  stopes  through 
winzes  put  down  from  the  level  above  and  spaced  100  feet 
apart  along  the  stopes,  its  distribution  being  done  in  small 
cars  operating  on  temporary  track  laid  on  the  waste. 

Owing  to  the  ore  chutes  having  become  badly  worn  it  is 
usually  found  necessary  to  run  ore  through  the  man-ways 
after  a  height  of  50  feet  has  been  reached  in  the  stope.  When 
the  stopes  have  reached  a  height  of  60  feet,  it  is  usually  con- 
sidered advisable  to  change  the  method  of  procedure  and 
remove  the  remaining  40  feet  by  overhand  stoping  and 
filling,  similar  to  the  filling  method  employed  in  the  mines 
at  Zaruma,  Ecuador.  Stoping  is  begun  at  the  foot  of  the 
winzes  and  carried  outward,  back-stopes  being  formed  as 
those  previously  driven  advance,  which  soon  forms  the  back 
into  faces  sloping  away  from  the  winzes.  Filling  is  run  in 
from  above,  providing  a  footing  for  the  miners  and  a  mount- 
ing for  the  drills.  The  back  may  also  be  supported,  if  found 
desirable,  by  props  or  cribs  built  on  the  sloping  sides  of  the 
fill.  Care  must  be  taken  as  the  levels  above  are  approached 


n6 


ORE  MINING  METHODS 


"I 

O 


MINING  IN  WIDE  VEINS  AND   MASSES  117 

or  the  timbering  in  them  may  collapse.     To  prevent  this 
the  back  is  removed  in  small  sections  and  cribs  placed 
beneath  the  level  timbers,  or  square-sets  may  be  employed. 
The  pillar-and-stope  method  of  mining  as  employed  in 
the  Central  Mine  is  applicable  to  great  width  of  lode  and  is 
now  operating  in  a  two  percent  ore-body.     The  ore-body 
is  developed  by  cross-cuts  run  from  levels  driven  in  the 
foot-wall,  which  are  connected  by  a  drift  or  level  running 
through  the  center  of  the  deposit.     S topes  are  opened  up 
from  the  level  in  the  lode,  which  are  run  across  the  lode  from 
wall  to  wall  50  feet  wide  (8  sets)  and  at  intervals  of  50  feet, 
thus  dividing  the  lode  into  stopes  and  pillars  alternately 
and  of  equal  width.     The  stope  sections  are  completely 
worked  out  on  the  sill-floor  and  carefully  timbered  with 
square-sets.     Winzes  are  then  put  in,  connecting  the  stopes 
with  the  level  above,  but  are  maintained  one-half  in  the 
pillar  and  one-half   in    the  stopes.     (See   Fig.   35.)     The 
outer  rows  of  sets  in  the  stopes  and  a  line  of  cross-cuts 
connecting  them  at  the  ends  of  the  stopes  are  kept  open 
by  lagging  on  the  sides  and  tops  of  the  sets.     All  other 
sets  with  the  exception  of  the  chute  sets  are  then  filled  with 
waste  and  the  work  of  stoping  out  the  back  is  begun.     This 
is  accomplished  by  the  open-stope  and  crib  method  pre- 
viously described,  the  ore  being  disposed  of  through  the 
chutes,  which  are  carried  up  to  the  full  height  of  the  stope. 
Waste  is  introduced  through  the  winzes  and  distributed 
throughout  the  stope,  filling  all  parts  except  the  two  side 
rows  of  sets,  which  are  carried  up  the  full  height  of  the  stope 
and  kept  open  in  order  that  the  waste  may  be  kept  clear 


n8 


ORE  MINING   METHODS 


of  the  pillars  and  to  permit  work  to  be  done  on  the  pillars 
if  desired.     The  stopes  are  worked  out  to  a  height  of  60  or 


70  feet,  after  which  the  arch  pillars  are  worked  out  by 
square-sets  and  filling. 

Owing  to  the  weight  of  the  ground,  which  will  have  begun 
to  settle  and  move  by  the  time  the  stopes  are  worked  out, 
all  of  the  pillars  on  one  level  are  robbed  at  one  and  the  same 


MINING  IN  WIDE  VEINS  AND  MASSES  119 

time,  which  is  accomplished  by  beginning  on  the  hanging- 
wall  side  of  the  lode  and  drifting  across  from  stope  to  stope, 
the  drifts  being  timbered  with  sets  and  filled  with  waste. 
From  the  face  thus  formed  the  work  of  stoping  then  proceeds 
both  horizontally  and  vertically  until  all  the  pillars  on 
a  level  have  been  removed,  the  space  being  filled  with 
square-sets  and  waste. 

While  the  idea  is  to  remove  ultimately  both  arch  and 
stope  pillars,  yet  such  large  quantities  of  ore  are  available 
with  less  work  and  danger  to  the  workings  that  so  far  little 
has  been  done  except  in  the  stopes  proper. 

The  open-stope  and  pillar-and-stope  methods  of  mining 
at  Broken  Hill  are  applicable  to  very  large  lodes  of  solid, 
low-grade  ore  and  with  fairly  strong  wall-rock.  High 
inclination  of  deposit  is  also  an  important  consideration  in 
working  by  these  methods. 

The  advantages  of  the  methods  are: 

1.  Large  outputs. 

2.  Low  cost  of  mining. 

3.  Comparatively  little  timber  required. 

4.  Labor  of  handling  waste  and  ore  slight. 

5.  Opportunity   afforded   for   sorting   ore   and   stowing 
waste. 

6.  Development  work  simple  and  not  extensive. 

7.  Ventilation  is  good. 

8.  Little  danger  of  accidents  from  falls. 

9.  The  complete  extraction  of  the  ore  is  aimed  at,  but 
not  attempted  at  present. 


120  ORE  MINING  METHODS 

The  disadvantages  of  the  method  are: 

1.  Applicable  only  to  large  deposits   of   low-grade  ore 
standing  at  high  dips. 

2.  Stopes  must  be  carried  vertically. 

3.  Stopes  are  of  limited  height,  usually  not  over  100  feet. 

4.  Loss  of  ore  in  pillars  large  even  if  ultimately  worked. 

There  are  few  mines  in  the  United  States  which  have 
experienced  so  many  changes  in  methods  of  working  as  have 
1  Homestake  Mine  ^  Homestake  mines  of  the  Black  Hills, 

Lead,  South       '  South   Dakota.     The   reason   for   this   is 


2.  Gold  Ore.  that  the  ores  are  low-grade,  ranging  from 

3.  Vein. 

4.  width  so  to       $2  to  $12  Per  ton>  and  to  operate  them 
50C  profitably  a  large  tonnage  and  low  cost 

of  mining  is  necessary. 

The  ore-bodies  are  broad  zones  of  impregnations  in  schists; 
they  are  quite  irregular,  varying  from  30  to  500  feet  in  width, 
and  usually  stand  vertically  or  nearly  so. 

Owing  to  the  great  width  of  the  deposits  the  stopes  are 
run  transversely,  extending  from  foot-  wall  to  hanging-  wall, 
pillars  being  left  between  the  respective  stopes.  Formerly 
it  was  customary  to  employ  square-sets  to  support  the  walls, 
which  combined  with  filling  permitted  the  stopes  to  be 
worked  to  a  height  of  85  to  100  feet,  the  latter  being  more 
usual.  It  was  found  that  square-sets  if  carried  above 
85  feet  would  often  collapse  under  their  own  weight.  With 
the  exhaustion  of  the  supply  of  suitable  timber  and  the  con- 
sequently increased  cost,  also  owing  to  the  gradually  de- 
creasing value  of  ore,  other  and  cheaper  methods  of  working 


MINING  IN  WIDE  VEINS  AND   MASSES  121 

the  ore-bodies  were  found  to  be  necessary.  While  the  general 
method  of  attack  has  not  changed  materially,  radical  changes 
in  support  have  been  made,  the  main  idea  apparently  being 
to  reduce  the  amount  of  timber  employed.  Timber  is  still 
used,  but  it  is  doubtful  whether  there  are  many  other  mines 
in  the  world  in  which  so  little  timber  is  actually  used  per 
ton  of  ore  extracted.  This  is  rendered  possible,  however, 
only  through  the  exceptionally  strong  and  solid  ore  and 
wall-rocks.  In  many  places  the  ore  stands  without  support 
in  low  arched  stopes  of  60  to  80  feet  in  width. 

Following  the  use  of  square-sets  and  filling,  a*  system  of 
back-filling  was  introduced,  being  first  employed  with  con- 
siderable timbering  in  the  form  of  timbered  passages  on  the 
ground  or  stope-floor,  but  as  the  work  is  now  carried  on  it 
would  seem  that  the  amount  of  timber  used  has  been  re- 
duced to  a  minimum.  This  has  been  rendered  possible  by 
a  rearrangement  of  the  drifts  and  cross-cuts  through  which 
the  ore  is  withdrawn  from  the  stopes. 

Descriptions  of  two  of  the  more  recent  methods  of  min- 
ing are  given  below  and  will  serve  to  illustrate  the  gradual 
change  that  is  being  made  in  these  mines. 

In  the  first  and  earlier  method  levels  are  driven  from  100 
to  150  feet  apart,  depending  largely  upon  the  condition  of 
the  ground  and  the  depth  of  the  workings.  The  levels 
having  been  formed  and  connected  by  foot-wall  and  hang- 
ing-wall drifts  and  one  or  more  intermediate  drifts,  the 
work  of  opening  up  the  stope  is  begun.  This  is  accomplished 
by  carrying  a  working  face  outward  and  across  the  deposit 
from  the  drift  on  the  foot- wall  side.  The  stope  is  cut  to  a 


122 


ORE  MINING  METHODS 


e 

§ 

(D 
| 

In 
o 

O 

ffi 

.2 

-s 

en 
•g 


b/J 


MINING  IN  WIDE  VEINS  AND  MASSES  123 

width  of  60  to  75  feet  and  to  a  height  of  about  10  feet,  the 
work  being  done  by  breast  stoping.  Other  stopes  are  begun 
along  the  line  of  the  level  drifts  at  intervals  of  25  to  40  feet, 
the  unworked  portions  serving  as  pillars  between  the  rooms 
or  stopes  on  either  side.  The  stope  having  been  cleared 
of  broken  ore,  all  lines  of  haulage  that  are  to  be  maintained 
in  the  stope  are  carefully  timbered  and  lagged.  The  pas- 
sages that  are  considered  necessary  for  the  proper  handling 
of  the  ore  are  sideways  and  endways,  the  former  being 
known  as  cross-cuts  and  the  latter  as  drifts.  The  drift  in 
the  foot- wall  side  is  timbered  with  a  double  row  of  sets. 
There  were  also  one  or  more  intermediate  passages  running 
transversely  with  the  stope  and  connecting  the  cross-cuts. 
(See  Figs.  36  and  37.) 

Back  stoping  is  then  begun,  usually  on  the  hanging-wall 
side,  and  carried  lengthwise  of  the  stope  for  a  width  of  about 
14  fet^t  less  than  that  of  the  first  or  level  stope.  By  this 
method  of  procedure  the  cross-cuts  are  set  into  the  pillars 
and  protected  by  them  from  movements  of  ore  in  the 
stopes.  No  attempt  is  made  to  remove  the  ore  as  it  is 
broken  down,  except  to  provide  space  for  the  miners  above, 
the  excess  being  drawn  off  from  below  along  the  line  of  the 
drifts  and  cross-cuts. 

As  the  height  of  the  stopes  increases  it  is  necessary  to 
provide  passages  for  the  men  to  and  from  them;  this  is 
accomplished  by  putting  in  raises,  which  are  in  line  with 
the  cross-cuts  and  like  them  are  set  into  the  pillars. 
These  raises  are  timbered,  and  besides  serving  as  man- 
ways  assist  in  ventilating  the  stopes.  With  levels  100  feet 


I24 


ORE   MINING   METHODS 


apart  the  stopes  are  carried  to  a  height  of  70  feet,  at  which 
point  the  roof  is  arched,  giving  an  additional  height  of 
15  feet,  thus  making  the  stopes  85  feet  high  and  leaving 
an  arch  pillar  15  feet  in  thickness.  With  greater  distance 


Fig.  37. —  End  View  of  Stope  in  Homestake  Mine,  Back-filling  Method. 
From  Model  in  Engineering  Office  of  Company. 

between  levels,  the  height  of  the  stopes  is  proportionally 
greater.  Finally  raises  are  put  through  the  arch  pillars  at 
the  highest  point  of  the  stope,  thus  establishing  communi- 
cation with  the  level  above.  These  raisers  are  subse- 


MINING   IN  WIDE  VEINS  AND   MASSES  125 

quently  employed   in   introducing  waste   into   the   stopes 
for  filling. 

The  work  of  stoping  having  been  completed,  the  ore 
may  be  withdrawn  or  left  in  the  stope  as  a  reserve  supply 
that  may  be  drawn  upon  as  occasion  demands.  It  is 
drawn  out  of  the  stope  by  breaking  away  the  lagging  on 
the  side  of  the  sets  on  the  foot-wall  side,  thus  permitting 
the  ore  to  run  into  the  drift,  where  it  is  shoveled  into  cars 
and  sent  to  the  shaft.  In  the  course  of  time  the  foot-wall 
end  of  the  stope  is  emptied  of  ore,  and  as  the  work  con- 
tinues the  shovelers  leave  the  shelter  of  the  timbered  drifts 
and  work  in  the  open  stope.  When  sufficient  room  has 
been  cleared  of  ore  the  work  of  filling  the  stope  is  begun 
and  continues  at  a  safe  distance  behind  the  shovelers.  It 
is  customary,  however,  to  cover  the  floor  of  the  stope 
with  old  timber  previous  to  placing  the  filling.  As  an 
extra  precaution  against  accidents  dams  are  often  erected 
to  check  and  hold  back  larger  pieces  of  waste.  (See  D, 
Fig.  36.)  The  filling,  as  previously  mentioned,  is  run 
into  the  stopes  through  the  waste  chutes  formed  in  the 
arch  pillars,  and  is  similar  in  many  respects  to  the  back- 
filling method  employed  in  the  Butte  mines.  Drawing 
ore  from  the  stopes  is  not  confined  to  the  drifts  and  inter- 
mediate passages,  but  may  be  carried  on  along  the  line 
of  the  cross-cuts.  The  ore  having  been  completely  drawn 
from  the  stope,  the  work  of  filling  is  continued  until  the 
curve  of  the  arch  is  reached,  when  the  filling  is  leveled 
preparatory  to  placing  square-sets,  which  are  employed  in 
removing  the  arch  pillars. 


126  ORE   MINING   METHODS 

The  arch  pillars  are  removed  by  overhand  stoping  and 
square-setting,  the  work  being  done  in  sections  running 
transversely  with  the  stope.  As  the  floor  of  the  stope 
above  is  approached  considerable  care  must  be  taken  to 
prevent  falls,  but  if  the  mat  of  timber  has  been  properly 
placed  there  is  not  much  danger,  provided  the  roof  is  re- 
moved in  small  sections.  As  each  section  across  the  stope 
is  cut  out  to  the  stope  above  and  timbered,  it  is  filled  with 
waste,  and  work  on  another  section  is  begun.  It  is  ob- 
viously necessary  to  sacrifice  the  timber  employed  in  re- 
moving the  arch  pillars,  which  is  practically  all  that  is  lost, 
the  parts  of  the  sets  employed  in  the  drifts,  cross-cuts  and 
raises  being  used  again  and  again  until  broken,  when  they 
are  employed  in  making  the  timber  mat. 

Owing  to  the  weakening  of  pillars  by  under-cutting  them 
for  the  cross-cuts  and  by  the  vertical  cuts  for  raises,  also 
for  reasons  of  economy  in  the  use  of  timber,  a  further 
change  was  considered  necessary.  The  present  method  of 
mining,  which  has  but  recently  been  introduced,  has  had 
these  objectionable  features  eliminated,  and  while  it  has  not 
probably  been  in  use  sufficiently  long  to  demonstrate  com- 
pletely its  success  and  adaptability  under  all  conditions,  it 
has  so  far  proven  amply  adequate  where  its  application 
seemed  advisable. 

In  this  method  the  ore-body  is  divided  into  stopes  and 
pillars,  the  former  being  60  feet  wide,  the  latter  42  feet, 
thus  giving  the  pillars  approximately  ico-foot  centers. 
Through  the  center  of  each  pillar  a  drift  6  feet  wide  is 
run,  from  which  cross-cuts  are  driven,  one  about  midway 


MINING  IN  WIDE  VEINS  AND  MASSES 


127 


V.;:(}:fiijj^'::;;:-;:-:"<:'-o  0)  \n'-'':.'-'i:, 

u 


128  ORE  MINING  METHODS 

of  the  pillar  and  the  others  spaced  at  intervals  of  30  feet 
on  either  side.  Only  one  drift  or  driveway  is  maintained  in 
the  stopes,  which  is  a  timbered  passage  extending  along  the 
hanging-wall  side,  the  main  drive  or  level  being  driven  in  the 
foot-wall  some  distance  from  the  deposit.  (See  Fig.  38.) 
Raises  are  put  up  as  timbered  passages  in  the  stopes  and 
at  points  opposite  the  cross-cut  openings,  but  on  one  side 
of  the  pillars  only.  They  are  placed  a  few  feet  distant 
from  the  pillars,  but  standing  wholly  within  the  stopes, 
and  are  surrounded  by  broken  ore.  Stoping  is  carried  on 
in  a  manner  similar  to  that  previously  described  for  the 
earlier  method  employed.  The  levels  are  usually  run  150 
feet  apart,  making  the  arched  stopes  some  135  feet  high. 
The  arch  pillars  are  removed  by  overhand  stoping  and 
square-sets. 

Ore  is  drawn  from  the  stopes  by  shoveling  from  the 
cross-cuts  and  driveways  connecting  the  drifts  in  the  pil- 
lars. The  stopes  in  this  method  of  mining  may  be  likened 
to  huge  ore  pockets,  the  cross-cuts  being  chutes  through 
which  the  ore  is  drawn  off.  Filling  follows  the  withdrawal 
of  the  ore,  beginning  with  the  hanging-wall  side,  its  introduc- 
tion into  the  stope  being  accomplished  as  described  for  the 
earlier  method.  It  is  the  intention  where  possible  to  re- 
move the  pillars  after  the  ore  has  been  drawn  and  the 
stopes  filled.  To  accomplish  this  to  the  best  advantage 
the  sides  of  the  pillars  are  laced  for  a  height  of  15  to  20 
feet,  beginning  with  the  floor,  which  is  done  before  filling 
the  stope  with  broken  ore  and  is  carried  upward  as  the 
stope  increases  in  height.  The  lacing  consists  of  8  by  8  inch 


MINING  IN  WIDE  VEINS  AND  MASSES  129 

timbers  placed  vertically,  to  which  slabs  and  planks  are 
spiked.  The  lacing  assists  in  holding  back  the  waste-filling 
and  prevents  the  mixing  with  the  ore  as  it  is  broken  in  the 
work  of  stoping  out  the  pillars.  Where  the  stope  extends 
above  the  lacing  the  waste  may  be  held  back  temporarily 
by  facing-boards  and  props.  Square-sets  may  be  employed 
in  removing  the  pillars.  (See  Fig.  39.) 

Considerable  ore  may  be  lost  in  drawing  the  ore  from 
the  stoped  pillars,  especially  during  the  latter  part  of  the 
operation. 

The  methods  of  mining  employed  in  the  Homestake 
mines,  and  as  described  above,  are  applicable  to  very  large 
deposits  of  low-grade  ore,  both  ore  and  wall-rock  being 
hard  and  strong,  permitting  wide  low-arched  stopes  to  be 
worked  with  safety. 

The  advantages  of  the  methods,  but  with  special  refer- 
ence to  the  latter,  are: 

1.  Levels  may  be  placed  a  considerable  distance  apart. 

2.  Little  timber  is  used. 

3.  Ore  is  broken  at  small  cost. 

4.  Shovelers  are  well  protected. 

5.  Filling  is  easily  and  cheaply  placed. 

6.  Percentage  extraction  high. 

7.  Amount  of  development  work  small. 

8.  Large  outputs  are  easily  obtainable. 
The  disadvantages  of  the  methods  are: 

1.  Applicable   only   to   wide    deposits   standing   nearly 
vertical. 

2.  The  work  must  be  carried  along  vertical  lines. 


130 


ORE  MINING   METHODS 


C/2 


MINING  IN  WIDE  VEINS  AND   MASSES 


3.  As  the  ore  breaks  in  large  masses  considerable  hand 
work  must  be  done  in  reducing  to  proper  size  to  be  loaded 
into  cars. 

4.  The  method  requires  considerable  handling  of  ore. 

5.  The  loss  of  ore  in  pillars  is  large  unless  they  are  ulti- 
mately removed 


132 


ORE  MINING  METHODS 


CAVING  METHODS 

During  the  comparatively  short  time  that  iron  ore  has 
been  mined  in  the  Lake  Superior  region  many  changes  in 

methods   have   been   made,  which    con- 

1.  No  Local  Applica- 

tion dition  of  affairs  has  been  brought  about 

2.  Iron  Ore.  .  ... 

3.  Massive  Deposits  largely   by  experience   in   mining   under 

4.  width  of  Veins  40  vai>i°us  conditions,  lack  of  suitable  timber 
to  so  ft.  anc|  a  demanci  for  cheaper  ore.      There 

are,  however,  two  methods  of  mining  that  have  been  em- 
ployed for  many  years,  and  while  modified  from  time  to 
time  to  meet  certain  conditions,  they  remain  fundament- 
ally the  same.  These  are  the  top-slice  and  sub-drift 
methods. 

No  local  application  will  be  made  in  the  descriptions  of 
these  methods,  other  than  to  state  that  they  are  applied 
equally  well  to  wide  veins  and  to  masses  covering  considerable 
areas.  Veins  ranging  in  width  from  40  to  80  and  100  feet 
and  with  dips  of  60  to  80°  may  be  readily  worked  by  both 
methods.  The  development  of  the  deposits  is  the  same, 
except  as  to  the  work  in  the  vein,  consisting  of  inclined  or 
vertical  shafts  sunk  in  the  foot-walls  of  veins  or  in  the  firm 
ground  some  distance  from  masses  of  ore,  levels  being 
50  to  75  feet  apart. 

In  the  top-slice  method,  after  the  cross-cuts  from  the 
shaft  have  reached  and  been  driven  into  the  deposit,  main 
levels  intersecting  them  are  run  through  the  center  of  the 
ore-body,  being  connected  at  intervals  of  100  feet  by  two 
compartment  raises.  These  raises  contain  an  ore  chute  and 
a  timber  chute  and  a  man-way,  the  last  two  being  the  same, 


MINING  IN  WIDE  VEINS  AND  MASSES  133 

and  are  put  up  to  barren  or  to  caved  ground  as  the  case 
may  be.  Beginning  at  the  top  of  a  raise  a  drift  is  run 
parallel  with  the  main  level  below  and  from  both  sides  of  the 
raise.  (See  Figs.  40  and  41.)  If  the  work  is  carried  on  sys- 
tematically these  drifts  should  meet  other  drifts  similarly 
driven  from  adjoining  raises,  or  encounter  caved  ground, 
the  ore  having  been  mined  out.  Cross-cuts  are  turned  off 
at  the  ends  of  the  drifts  and  the  ore  removed  to  the  vein- 
walls.  These  drifts  and  cross-cuts  must  be  carefully  tim- 
bered, the  sets  often  being  given  double  posts.  The  ore  is 
hauled  to  the  chute  in  small  cars  and  in  some  cases  handled 
in  wheelbarrows.  The  cross-cuts  having  been  run  to  the 
walls,  a  mat  of  timber  is  placed  on  the  floor,  consisting  of 
three  long  stringers  laid  near  the  foot  of  the  posts  of  the 
sets  and  midway  between  them,  upon  which  in  turn  are 
placed  split  lagging  and  slabs.  This  mat  of  timber  sup- 
ports the  caved  material  when  a  drift  is  run  beneath  it. 
To  facilitate  the  work  of  placing  the  mat,  the  cross-cuts 
are  driven  in  only  one  direction  at  a  time,  thus  permitting 
the  placing  of  the  mat  in  the  finished  cross-cuts  on  one 
side  of  the  drift.  (See  Plan  of  top-slice,  Fig.  41.)  The 
mat  having  been  placed,  the  sets  are  blasted  out,  permitting 
the  roof  to  cave  close  up  to  the  ends  of  the  pillars.  Other 
cross-cuts  are  then  opened  up  at  the  ends  of  the  drifts 
adjacent  to  the  caved  ground,  the  same  process  of  cutting 
out,  timbering,  placing  mat  and  caving  the  ground  being 
repeated.  This  is  continued  until  the  pillars  are  entirely 
removed,  when  the  drift  is  of  necessity  closed  and  a  new 
drift  is  opened  up  at  the  top  of  the  raise  as  was  previously 


134 


ORE  MINING  METHODS 


LONGITUDINAL  ELEVATION 
TOP-SLICE 


Fig.  41.— Plan  and  Longitudinal  Section  of  Top-slice  Method. 


MINING  IN  WIDE  VEINS  AND  MASSES  135 

done,  and  work  on  a  new  slice  is  begun.     Timber  is  hoisted 
through  the  man-ways  to  the  slicing  drifts. 

The  top-slice  method  is  applicable  to  large  bodies  of 
cheap  ore,  which  may  be  hard  or  moderately  soft.  If  veins 
are  worked  they  should  have  a  dip  not  less  than  60°. 

The  advantages  of  the  method  are: 

1.  Development  is  simple  and  quickly  done. 

2.  Opportunity  is  afforded  for  sorting  ore,  as  keeping 
Bessemer  and  non-Bessemer  ores  separate.  , 

3.  Practically  the  complete  extraction  of  ore  is  possible. 

4.  Ventilation  is  good. 

5.  Little  danger  of  accidents  from  falls. 

6.  Cost  of  mining  is  low. 

The  disadvantages  of  the  method  are: 

1.  Number  of  working  places  limited,  thus  limiting  out- 
put. 

2.  Levels  close  together. 

3.  Considerable  timber  required. 

4.  Much  handling  of  ore  and  timber. 

5.  Confined  to  deposits  close  to  the  surface. 

The  sub-drift  method,  while  employed  in  the  same  district 
and  even  in  the  same  mines  as  the  top-slice,  differs  radically 
from  it  both  in  methods  of  development  and  in  working. 
The  development  of  a  wide  lode  which  is  to  be  worked  by 
the  sub-drift  method  is  shown  in  Fig.  42.  A  main  level 
is  run  in  the  deposit,  near  the  foot-wall,  connecting  the 
points  where  the  cross-cuts  from  the  shaft  enter  the  lode, 
from  which  drifts  are  driven  at  intervals  of  about  50  feet, 


136  ORE  MINING  METHODS 

cross-cutting  the  lode.  A  second  main  level  is  then  run 
along  close  to  the  hanging-wall  and  connected  with  the 
cross-cutting  drifts.  The  ore  on  the  levels  is  cut-up  by  means 
of  the  drifts  and  levels  into  blocks  some  50  feet  long  and  the 
full  width  of  the  lode.  At  5o-foot  intervals  along  the  line 
of  the  main  levels,  raises  are  put  up  from  which  other  drifts 
are  driven,  forming  the  so-called  sub-drifts.  Beginning  at 
a  lower  level  than  is  being  worked,  a  raise  is  put  up  for  a 
height  of  6  or  8  feet  and  timbered,  after  which  two  drift  sets 
are  placed  and  lagged  over,  thus  forming  the  starting  point 
of  sub-drifts  which  are  driven  in  both  directions,  ultimately 
making  connection  with  other  drifts  driven  from  adjoining 
raises.  As  soon  as  the  '  subs  '  are  well  started  the  raise  is  put 
up  another  6  or  8  feet  and  a  second  set  of  subs  is  begun. 
The  operation  of  putting  up  raises  and  driving  subs  is  con- 
tinued until  the  raises  break  through  into  the  level  above 
and  the  subs  have  made  connection  with  other  subs.  It 
is  then  evident  that  when  all  the  subs  and  raises  have  been 
completed  the  ore  between  two  adjoining  levels  is  honey- 
combed by  both  horizontal  and  vertical  passages  and  is 
ready  for  the  last  stage  of  the  operation  of  extraction  of 
the  ore.  Sub-drifting  is,  then,  preliminary  development 
work  in  the  deposit  itself,  and  is  an  intermediate  operation 
between  the  opening  of  the  deposit  by  shafts,  cross-cuts, 
levels,  etc.,  and  the  actual  work  of  breaking  down  the  ore. 
(See  Fig.  43.)  The  height  of  the  respective  subs  is  the 
distance  from  the  floor  of  one  to  that  of  another  directly 
above  it,  and  varies  from  12  to  15  feet,  depending  largely 
upon  the  character  and  condition  of  the  ore. 


MINING  IN  WIDE  VEINS  AND  MASSES 


137 


CROSS-SECTION  SUB-DRIFT 

Fig.  42. —  Section  through  Lode  showing  Method  of  Development  in 
Sub-drift  Method. 


138  ORE   MINING  METHODS 

The  work  of  sub-drifting  is  followed  by  the  removal  of 
ore  from  the  pillars  standing  between  the  subs  and  the 
drifts,  also  that  standing  in  the  back  above  the  level  of  the 
tops  of  the  subs,  and  is  commonly  known  as  l  stripping.' 
Consider  that  the  work  of  stripping  has  reached  the  point 
shown  in  the  longitudinal  section,  Fig.  43.  By  knocking 
down  the  supporting  posts,  as  shown  at  the  left  of  the  first 
sub,  the  back  of  ore  will  fall  and  can  be  shoveled  up  and 
hauled  away  to  the  chutes.  The  settlement  of  the  broken 
rock  above  is  controlled  by  the  mat  of  timbers  which  is 
constantly  being  added  to  by  the  timbers  in  the  subs  that 
are  lost  and  broken.  The  method  of  cutting-out  the  pillars 
is  shown  in  the  plan,  Fig.  43,  as  at  the  left  where  the 
stubs  of  pillars  are  being  removed,  the  back  standing  on 
posts.  As  a  sub  cannot  be  worked  beneath  others  not 
yet  removed,  it  is  necessary  to  either  entirely  remove 
the  upper  sub  before  beginning  work  on  a  lower  one, 
or  to  carry  on  the  stripping  in  descending  order,  each 
sub  being  carried  some  distance  in  advance  of  the  one 
below. 

As  soon  as  the  stripping  operation  reaches  a  main  level 
that  level  is  abandoned  and  all  communication  with  the 
subs  below  must  be  through  the  lower  level.  The  usual 
practice  is  to  have  one  level  or  lift  (the  block  of  ore  between 
levels)  in  the  process  of  stripping;  the  next  lower  sub- 
drifting,  while  the  third  lift  below  is  being  opened  up  by 
cross-cuts.  The  ore  will  also  have  to  be  run  through  the 
chutes  from  the  upper  to  the  lower  sub.  In  order  to  facili- 
tate the  handling  of  timber  it  is  brought  in  from  the  upper 


MINING  IN  WIDE  VEINS  AND  MASSES  139 

level  and  lowered  to  the  respective  subs  instead  of  being 
raised  as  in  the  top-slice  method. 

Light  but  close  timbering  is  the  rule  and  by  careful  work 
the  caving  ground  can  be  controlled  with  little  or  no  danger 
of  crushes  and  loss  of  ore. 

The  work  of  mining  by  the  sub-drift  method  as  described 
is  for  comparatively  hard  and  strong  formations,  but  when 
soft  and  unstable  formations  are  encountered,  either  the 
method  will  have  to  be  modified  to  meet  the  special  condi- 
tions or  a  change  of  method  will  be  necessary.  The  method 
of  working  by  sub-drifting  as  employed  at  the  Susquehanna 
Mine  at  Hibbing,  Minnesota,  is  shown  in  Fig.  44. 

On  approaching  the  limits  of  the  ore-bodies  in  this  mine 
masses  of  clay  and  sand  are  encountered,  which  unless  care- 
fully controlled  will  break  into  and  fill  the  workings.  A 
block  of  ore  is  shown,  the  opening  up  of  which  has  developed 
the  bad  condition  of  the  ground,  which  is  under  control  by 
the  employment  of  dams  in  the  drifts  and  cross-cuts  and 
even  at  the  face  where  stripping  is  being  done.  Two  sets 
of  dams  are  shown,  which  were  found  necessary  in  order  to 
hold  back  the  clay  and  sand.  The  dams  are  built  of  one- 
inch  pine  boards  strongly  reenforced  by  backing  strips  and 
braces.  The  method  of  attacking  the  pillars  is  shown  by 
the  arrows.  The  back  varies  from  8  to  12  feet  in  thickness, 
and  is  caved  by  blasting  out  three  sets  at  a  time,  thus  bring- 
ing the  cave  to  within  one  set  of  the  working  face.  The 
timber  used  for  sets  in  this  mine  is  8  to  10  inches  in  diameter, 
the  floor  being  covered  with  rough  pine  boards  upon  which 
the  sets  stand.  These  boards  render  shoveling  easy  and 


140 


ORE   MINING   METHODS 


PLAN  OF  THIRD   SUB-DRIFT 

Fig.  43. —  Longitudinal  Section  and  Plan  of  Sub-drift  Method. 


MINING   IN  WIDE  VEINS  AND   MASSES  141 

make  a  good  mat  in  controlling  the  movement  of  broKen 
ground  and  waste  ore. 

The  sub-drift  method  of  mining  is  applicable  to  both 
hard  and  moderately  soft  ores,  preferably  the  former,  but 
not  to  mixed  ores  as  where  Bessemer  and  non-Bessemer  ores 
occur  together.  It  is  strictly  large-scale  work  and  may  be 
applied  to  massive  deposits  or  large  lodes  of  cheap  ore. 

The  advantages  of  the  method  are: 

1.  Large  outputs  are  possible  owing  to  the  large  number 
of  points  of  attack. 

2.  Cost  of  mining  low. 

3.  The  complete  extraction  of  ore  practically  possible. 

The  disadvantages  of  the  method  are: 

1.  Much  timber  is  required. 

2.  Development  work  extensive  and  complicated. 

3.  Little  or  no  opportunity  afforded  for  sorting  ore. 

4.  Considerable  handling  of  ore  and  timber  necessary. 

5.  Ventilation  is  poor. 

6.  Stripping  operation  rather  dangerous. 

7.  Confined  to  deposits  lying  close  to  the  surface. 

8.  Limited  to  comparatively  hard  ores. 

Of  the  various  methods  of  mining  in  use  in  the  Bingham 
Canyon  mines,  that  employed  by  the  Utah  Copper  Com- 
pany is  both  ingenious  and  efficient,  if  one  ±  Utah  copper  Co.'g 
can  judge  by  the  speed  and  facility  with 


which  cars  are  loaded  and  handled.  3*  Sassfve  Deposit. 

The  caving  method  referred  to  above  4'  Very  Extensive- 
is    employed    at    a    point   opposite    the    extensive    steam 


142 


ORE   MINING   METHODS 


MINING   IN  WIDE  VEINS  AND   MASSES  143 

shovel  workings.  It  is  employed  in  working  the  porphyry 
ore,  which  averages  1.8  per  cent  copper.  The  extent  of  the 
deposit  is  stupendous,  varying  in  thickness  from  100  to  300 
feet  and  reaching  practically  from  center  to  center  of  the 
mountains  on  either  side  of  the  Canyon.  It  is,  then,  evident 
that  there  is  practically  an  unlimited  field  for  the  develop- 
ment of  a  method  of  mining,  which  should,  however,  be 
extensive,  systematic  and  economical  in  operation. 

The  deposit  is  opened  up  by  a  tunnel  which  connects  on 
the  main  level  with  a  system  of  drifts  and  cross-cuts  by 
means  of  which  a  certain  area  is  subdivided  into  blocks 
averaging  probably  50  to  75  feet  square.  This  preliminary 
development  work  is  essential,  as  it  determines  the  lateral 
extent  of  the  workings  above,  and  facilitates  handling  ore. 
The  same  method  of  procedure  is  followed  on  each  main 
level,  of  which  there  are  only  two  in  this  mine,  the  levels 
being  200  feet  apart.  From  the  main  levels,  raises  or  chutes 
are  put  up  30  to  33  feet  vertically,  after  which  they  are 
driven  at  an  angle  of  55°  with  the  horizontal.  These  main 
raises  or  chutes  usually  extend  to  cap-rock,  and  often  break 
through  on  the  surface,  providing  good  ventilation.  At 
intervals  of  30  to  35  feet,  usually  33  feet,  sub-levels  or  subs 
are  opened  from  the  sides  of  the  raises,  which  are  in  turn 
connected  by  cross-cuts,  forming  roughly  square  pillars 
50  to  75  feet  in  size.  (See  Figs.  45  and  46.)  Branch 
raises  or  chutes  are  then  driven  at  angles  of  50  to  55°  with 
the  main  raises,  making  connection  with  midway  or  inter- 
mediate points  in  the  subs  and  cross-cuts,  thus  facilitating 
the  handling  of  ore  in  the  blocked-out  ground.  When  all 


144 


ORE  MINING  METHODS 


SHOOTS  JO 

HOnOUHl  NOIJ.03S         g 


a 

<u 

Q 


S13A31    NIVIAI 
QNtf  S13A3 
HOHOdHl  NOIJ.03S 


MINING   IN  WIDE  VEINS  AND  MASSES  145 

raises  and  subs  have  been  driven,  the  space  between  two 
levels  or  a  lift  is  ready  to  be  caved. 

Caving  is  accomplished  by  beginning  on  the  upper  sub- 
level,  which  underlies  the  capping  or  caved  ground,  and 
enlarging  the  ends  of  the  raises  or  chutes  and  finally  placing 
and  firing  shots  in  order  to  start  a  cave.  A  certain  part 
of  the  blocked-out  ground  can  by  this  means  be  broken  up 
and  run  to  the  main  level  below.  Further,  considerable 
ore  can  be  obtained  by  cutting  out  or  milling  about  the 
mouths  of  raises  or  chutes,  but  this  is  only  done  in  strong 
ground.  To  facilitate  the  work  of  caving  and  drawing  off 
the  pillars  other  raises  are  driven  into  them  from  the  drifts 
and  cross-cuts,  which  when  caved  will  have  removed  the 
larger  part  of  the  pillars,  leaving  a  roughly  shaped  pyramid. 
These  stub  pillars  can  only  be  attacked  to  advantage  from 
below,  which  is  done  by  cross-cutting  the  pillar  with  a  drift 
and  from  the  center  putting  up  four  inclined  raises  running 
upward  and  outward  toward  the  four  sides  of  the  pillar. 
(See  Fig.  46.)  These  raises  are  in  turn  caused  to  cave,  and 
the  ore  that  cannot  be  obtained  from  them  is  usually  left 
to  be  worked  with  and  from  the  sub  below.  All  raises  run 
in  the  pillars  are  provided  with  ore  chutes  and  gates  in 
order  that  the  flow  of  ore  may  be  controlled  and  properly 
loaded  into  cars. 

It  is  necessary  to  carefully  timber  all  drifts  and  cross-cuts 
before  beginning  to  cave  and  draw  off  the  ore,  otherwise  a 
crush  may  start  and  get  beyond  control  of  the  miners. 

The  caved  ground,  following  the  ore  downward,  soon 
reaches  a  point  near  the  exhaustion  of  the  pillars,  where  it 


146  ORE  MINING  METHODS 

begins  to  mix  with  the  ore;  the  timbered  passages  also  begin 
to  show  the  effect  of  excessive  pressure,  thus  indicating  that 
that  portion  of  the  sub  at  least  will  have  to  be  abandoned. 
Work  is  then  begun  on  a  lower  sub  and  carried  on  in  a 
manner  similar  to  that  described  above.  The  caving  of  all 
ore  above  a  sub  progresses  away  from  the  boundary  of  the 
property  and  from  above  downward,  from  sub-level  to  sub- 
level,  until  a  main  level  is  reached,  when,  if  it  has  been  pre- 
viously opened  up  by  raises  and  sub-levels,  work  upon  it  may 
be  begun. 

It  is  obviously  impossible  to  prevent  the  mixing  of  ore 
and  waste  during  certain  parts  of  the  work,  especially  just 
before  abandoning  a  sub-level,  but  that  is  an  evil  attendant 
upon  all  similar  operations,  particularly  large-scale  work. 
The  nicety  with  which  the  work  can  be  controlled  and 
the  ease  and  rapidity  with  which  the  ore  can  be  handled 
in  the  subs  are  the  really  astonishing  features  of  the 
method. 

A  very  important  consideration  looking  to  the  proper 
working  of  the  method  is  the  method  of  driving  raises  on 
the  incline  rather  than  vertically,  the  advantage  being  that 
there  is  much  less  likelihood  of  the  raises  becoming  choked 
up  with  ore,  as  it  slides  to  the  vertical  portion  and  then  falls 
in  a  loose  mass,  which  can  readily  be  drawn  off  and  does  not 
pack. 

The  branched-raise  caving  method  as  briefly  described 
above  is  applicable  to  very  large  deposits  of  low-grade  ores 
which  are  both  solid  and  strong  and  sufficiently  close  to  the 
surface  to  permit  the  caving  of  the  overburden. 


MINING  IN  WIDE  VEINS  AND  MASSES 


147 


I 

bfl 

.s 

O 


•O 

Tf 

bb 


148  ORE  MINING  METHODS 

The  advantages  of  the  method  are: 

1.  Large  outputs  are  possible. 

2.  Mining  cost  is  low. 

3.  Little  timber  is  required  except  in  caving  sub-levels. 

4.  Ore  is  handled  with  little  labor. 

5.  Main  levels  can  be  placed  a  considerable  distance  apart. 

6.  Danger  of  falls  is  slight. 

7.  Ventilation  is  good. 

The  disadvantages  of  the  method  are: 

1.  Applicable  to  large  deposits  only. 

2.  Large  amount  of  development  work  is  necessary. 

3.  Loss  of  ore  is  considerable  and  value  of  ore  occasionally 
reduced  by  mixing  of  waste. 

4.  Considerable  timber  is  lost  in  caving. 

The   diamond  mines   of   South   Africa   are  particularly 

interesting  from  the  standpoint  of  economic  mining,  which 

has  been  rendered  possible  by  the  appli- 

1.  Kimberly  Dia- 
mond Mines,        cation  of  a  caving  system  operated  on  a 

South  Africa. 

2.  Diamond-bearing  large    scale.     The   deposits   of   diamond- 
3    Pipes.  bearing  material  occur  in  ducts  or  pipes 
4.  Several  acres  in     wnich  stand  vertically  or  nearly  so  and 

lateral  extent.  J  J 

penetrate  a  number  of  formations  for  a 
known  depth  of  several  thousand  feet.  (See  Figs.  48  and  49.) 
The  pipes  are  roughly  round  or  oval  in  shape,  and  vary  in 
area  at  the  surface  from  a  few  to  50  acres.  The  walls  with 
the  exception  of  the  black  shale  are  fairly  strong  and  stand 
well.  The  shale  presents  the  greatest  difficulty  to  mining, 
as  it  weathers  rapidly  and,  falling  into  the  open-cuts,  fol- 


MINING  IN  WIDE  VEINS  AND   MASSES 


149 


lows  the  diamond-bearing  ground  downward  as  it  is  mined 
out  from  below.  For  plan  see  Fig.  47. 

In  order  that  the  method  of  mining  now  employed  in 
these  mines  may  be  readily  understood,  as  well  as  the  rea- 
son for  its  employment  we  shall  describe  the  method  of 
working  by  galleries  as  previously  employed. 

The  pipes  were  intersected  by  tunnels  extending  from  shafts 


ORE  MINING  METHODS 


•a 


MINING  IN  WIDE  VEINS  AND  MASSES 


152  ORE  MINING  METHODS 

sunk  in  the  rim-rock,  which  tunnels  were  spaced  150  to  200 
feet  apart,  thus  establishing  levels  in  the  deposits.  Inter- 
mediate levels  were  run  from  winzes  connecting  the  main 
levels  and  spaced  30  feet  apart  vertically.  On  each  level  two 
or  more  tunnels  were  driven  parallel  with  the  axis  of  the 
deposit  and  spaced  120  feet  apart.  From  these  tunnels 
galleries  18  feet  wide  and  high  were  driven  at  intervals 
of  36  feet,  and  were  worked  to  within  12  feet  of  the  level 
above,  and  the  uppermost  to  within  12  feet  of  the  loose 
ground.  (See  Fig.  48.)  Beginning  just  below  the  loose 
ground  the  roof  and  pillars  of  an  intermediate  level  were 
carefully  and  systematically  robbed,  thus  permitting  the 
caved  ground  above  to  settle  without  danger  of  a  crush. 
This  method  of  procedure  proved  fairly  successful  until 
considerable  depth  was  reached,  when  the  roofs  of  the 
galleries  became  unsafe  and  often  collapsed,  rendering  the 
extraction  of  the  diamond-bearing  ground  both  difficult 
and  dangerous.  Could  timber  have  been  employed  the 
method  would  have  proven  much  more  satisfactory  and 
would  have  been  applicable  to  much  greater  depths.  The 
method  proved  to  be  both  expensive  and  dangerous  and 
was  superseded  by  a  form  of  sub-drift  caving. 

In  the  new  caving  system  the  method  of  opening  up  or 
developing  the  pipes  is  the  same  as  described  in  the  gal- 
lery system  of  working,  with  the  possible  exception  that 
the  intermediate  levels  or  sub -drifts  are  somewhat  further 
apart,  ranging  from  30  to  40  feet.  (See  Fig.  49.)  From 
the  main  tunnels  running  along  the  major  axis  of  the  de- 
posit, drifts  are  driven  at  3o-foot  intervals,  being  extended 


MINING  IN  WIDE  VEINS  AND   MASSES 


Fig.  50. —  Elevations  and  Plans,  showing  Method  of  Opening  up  a  Stope. 

to  the  limits  of  the  deposit.  (See  Fig.  47.)  These  drifts 
are  enlarged  both  horizontally  and  vertically  by  stoping 
until  they  are  connected,  thus  forming  long  chambers  or 
stopes.  The  various  stages  of  opening  a  stope  are  shown 
in  Figs.  50  and  51.  The  roofs  of  the  intermediate  levels 
are  cut  out  by  overhand  stoping,  the  men  standing  upon 
the  broken  ground  while  drilling.  As  the  work  of  stoping 
proceeds  and  the  face  of  one  stope  recedes  from  the  wall- 
rock  another  stope  is  broken  through  from  below,  and  so 
on  until  a  number  of  stopes  are  worked,  each  level  pro- 
ceeding upward,  being  in  advance  of  the  one  below,  thus 


154 


ORE  MINING  METHODS 


Fig.  51.— Sketch  showing  Plan  of  Slopes  run  together. 

forming  terraces.  (See  Fig.  52.)  The  diamond-bearing 
ground  falling  upon  the  loose  ground  flows  downward  to 
the  floor  of  the  level  below,  where  it  is  shoveled  into  cars. 

The  method  of  mining  employed  in  the  diamond  mines 
of  South  Africa  is  applicable  to  large  deposits  of  consid- 
erable vertical  extent  and  to  ground  of  varying  degrees  of 
hardness  but  all  moderately  strong. 

The  advantages  of  the  method  are: 

1.  Little  or  no  timber  is  used. 

2.  Large  outputs  are  possible. 

3.  The  cost  of  mining  is  low. 

4.  Levels  can  be  placed  a  considerable  distance  apart. 

5.  Complete  extraction  of  valuable  ground. 

6.  Little  danger  from  falls  of  ground. 
The  disadvantages  of  the  method  are: 

i.  Can  be  employed  to  advantage  only  on  a  large  scale. 


MINING  IN  WIDE  VEINS  AND  MASSES 


Fig.  52  —Vertical  Section,  showing  Stopes  in  Various  Stages  of  Working. 

2.  The  amount  of  development  is  large. 

3.  Loss  from  valuable  ground  mixing  with  waste  is  con- 
siderable at  times. 

4.  Ventilation  is  rather  complicated. 

5.  Danger  from  mud-rushes. 


CHAPTER  V 

OPEN-CUT  MINING 

INTRODUCTION 

THE  surface  working  of  ore  deposits  is  confined  to  out- 
crops of  veins  and  ore-bodies  with  little  or  no  cover.  It 
may  be  considered  as  the  initial  or  preliminary  method  of 
extracting  ore  from  such  deposits,  and  is  at  the  same  time 
an  inexpensive  and  rapid  method  of  procedure.  Unless 
especially  advantageously  situated,  as  on  the  side  of  a  con- 
siderable elevation  or  mountain,  where  the  deposit  can  be 
attacked  at  different  levels,  the  work  of  open-cut  mining  is 
limited  to  comparatively  shallow  depths.  Depths  of  several 
hundred  even  up  to  500  feet  have,  however,  been  attained. 
The  Swedish  iron  mines  have  depths  of  400  and  500  feet;  the 
diamond  mines  of  Kimberley,  South  Africa,  were  some  400 
feet  deep  when  open-cut  work  was  abandoned;  the  Tilly 
Foster  iron  mine  was  worked  to  a  depth  of  over  300  feet; 
the  Iron  Mountain  Mine  of  Missouri  reached  a  depth  of 
150  odd  feet  before  being  abandoned;  the  Rio  Tinto  mines 
of  Spain  are  very  extensive  both  as  to  depth  and  lateral 
extent;  the  slate  quarries  of  Wales  have  reached  a  depth 
of  600  feet;  etc.  Many  other  instances  of  deep  open- 
cut  mining  might  be  mentioned,  such  as  the  Homestake 

mines,  South  Dakota,  and  the  Alaska-Treadwell  mines  of 

156 


OPEN-CUT  MINING  157 

Douglas  Island,  Alaska,  but  these  mines  may  be  con- 
sidered as  having  passed  the  stage  of  open- cut  work  inas- 
much as  the  ore  is  not  removed  from  the  surface  excava- 
tion, except  to  a  very  limited  extent,  but  is  drawn  off 
underground  through  the  mine  workings. 

The  extension  of  the  surface  working  of  ores  to  great 
depths  by  combining  such  work  with  the  underground 
operations  has  led  to  the  employment  of  a  most  interest- 
ing and  important  method,  namely,  'Glory-hole'  mining. 

The  method^  of  open-cut  mining  that  are  more  or  less 
extensively  employed  in  the  extraction  of  ore  and  similar 
materials  may  be  grouped  under  the  following  heads: 
surface  mining  by  hand;  surface  mining  by  scrapers;  open- 
cut  mining  by  steam  shovels,  and  the  milling  method.  As 
outlined  above  the  methods  of  open-cut  mining  are  dis- 
cussed in  order  of  importance,  i.e.,  extent  and  complexity 
of  operations.  Stripping  and  mining  by  hand  and  scrapers 
are  confined  largely  to  working  coal  outcrops  and  super- 
ficial deposits,  while  steam-shovel  work  and  the  milling 
methods  are  employed  on  a  large  scale  in  mining  both  base 
and  precious  metals. 

While  it  is  the  purpose  of  this  work  to  discuss  methods 
of  mining  of  ores,  yet  it  seems  advisable  and  almost  neces- 
sary in -this  connection  to  refer  to  the  working  of  certain 
non-metalliferous  materials  in  order  to  properly  illustrate 
the  methods  as  outlined  above.  This  is  particularly  true 
of  surface  work  by  hand  and  scrapers,  although  practically 
all  ores  are,  in  certain  localities,  mined  in  a  limited  way  by 
such  methods. 


158  ORE   MINING   METHODS 

SURFACE  MINING  BY  HAND 

Wherever  large  veins  and  masses  of  workable  ore  occur 
at  the  surface,  or  with  a  thin  cover  of  barren  material  or 
wash,  it  is  customary  to  employ  some  method  of  surface 
working,  the  extent  of  such  operations  depending  upon  the 
size  of  the  deposit.  With  veins  especially,  the  amount  of 
ore  is  usually  rather  limited  or  the  position  of  the  deposit 
is  such  as  to  preclude  any  but  hand  work.  On  the  other 
hand  massive  deposits  of  low-grade  ore  or  certain  non- 
metalliferous  materials  may  be  worked  to  advantage  by 
hand.  The  mining  of  shale  for  use  in  the  manufacture  of 
Portland  cement  is  shown  in  Fig.  53.  The  shale  beds 
are  loosened  by  hand  drilling  and  blasting,  the  broken-up 
shale  being  loaded  into  carts  and  wagons  and  hauled  some 
distance  to  the  plant. 

The  application  of  hand  work  to  a  large  outcrop  of  work- 
able ores  may  be  illustrated  by  a  common  method  of  work- 
ing a  bank  of  iron  ore  which  is  to  be  loaded  into  railroad 
cars  for  transference  to  some  distant  point.  The  railroad 
track  having  been  established  at  a  certain  level,  a  dock  is 
built  up,  provided  no  excavation  is  necessary  for  bringing 
the  track  to  the  deposit,  otherwise  it  could  be  employed  to 
advantage  for  a  dock.  The  height  of  the  dock  should  be 
such  that  hand  cars  can  be  dumped  from  it  into  the  rail- 
road cars  below.  Upon  the  dock  a  series  of  hand-car  tracks 
are  laid  practically  parallel  to  each  other  and  normal  to 
the  face  of  the  bank  of  ore  to  be  excavated.  The  bank  is 
blasted  down  and  the  ore  loaded  by  hand  into  the  small 


OPEN-CUT  MINING 


159 


160  ORE   MINING   METHODS 

hand  cars,  which  operate  back  and  forth  between  the 
bank  and  the  dock,  the  grade  of  the  tracks  being  slightly  in 
favor  of  the  loaded  cars.  In  this  manner  a  number  of 
railroad  cars  can  be  loaded  at  one  and  the  same  time,  and 
until  the  face  of  the  bank  has  receded  to  a  point  some 
distance  from  the  dock,  large  outputs  at  low  cost  are 
possible. 

Hand  work  has  its  widest  application  in  earth  excava- 
tion or  the  working  of  other  more  or  less  soft  and  easily 
disintegrated  materials,  in  the  working  of  which  it  has 
reached  its  greatest  utility.  High  banks  of  earth  are 
formed  into  terraces  sufficiently  wide  for  wagons  or  cars  to 
operate  upon  and  of  such  a  height  as  to  permit  the  control 
of  the  loosened  material.  The  faces  of  the  terraces  are 
attacked,  being  divided  into  sections  by  vertical  cuts  and 
undermined  by  horizontal  cuts  made  at  the  bottom  of  the 
bank  or  terrace.  The  remaining  outstanding  portions  of 
the  bank  are  then  broken  down,  by  bars,  a  line  of  holes 
being  made  along  the  top  of  the  bank  parallel  with  the  edge 
and  connecting  the  vertical  cuts.  Large  masses  of  the 
bank  are  thus  broken  down,  and  in  the  fall  to  the  level 
below  are  readily  broken  into  a  convenient  size  for  shovel- 
ing. While  rock  and  ore  formations  differ  radically  from 
earth  and  other  similar  materials,  yet  the  same  general 
method  of  procedure  is  applicable.  Terraces  are  usually 
formed  upon  which  the  men  stand  while  drilling  holes, 
explosives  being  used  in  breaking  down  the  face  of  the 
banks.  Large  or  mammoth  blasts  may  be  employed  in 
breaking  down  high  banks,  which  necessitate,  however, 


OPEN-CUT  MINING 


161 


considerable  preparatory  work  in  the  shape  of  drilling  or 
tunneling  and  placing  and  preparing  the  blasts. 

The  application  of  open-cut  work  to  the  quarrying  of  rock 
is  shown  in  the  frontispiece,  also  in  Figs.  54  and  55,  the 
figures  showing  the  condition  of  the  bank  before  and  after 
firing  a  large  charge  of  explosives,  while  the  frontispiece 


Fig.  54. —  Quarry  showing  Bench  before  Blast. 

shows  the  appearance  of  the  quarry  at  the  time  of  the 
explosion. 

In  the  present  day  of  keen  competition  and  large-scale 
operations  all-hand-work,  i.e.,  breaking  down  the  ore  and 
loading  by  hand,  is  fast  becoming  a  thing  of  the  past,  al- 
though it  is  still  used  in  many  localities,  as  in  the  soft-iron 


162 


ORE   MINING   METHODS 


mines  of  Alabama,  where  the  ore  is  easily  handled  and  labor 
is  cheap. 

Surface  mining  by  hand  is  applicable  to  moderate-sized 
and  large  deposits  occurring  without  a  cover  or  with  covers 
of  limited  thickness.  While  hard  and  soft  materials  can 
be  handled,  a  material  that  will  break  up  into  moderately 


Fig.  55. —  Quarry  showing  Result  of  Blast. 

small  pieces  is  preferable,  as  it  is  more  readily  loaded  into 
cars  or  wagons  by  shovel. 

The  advantages  of  hand  work  in  open  cuts  are: 

1.  The  expenditure  for  equipment  is  slight. 

2.  There  is  little  depreciation  of  equipment  either  when 
the  mine  is  operating  or  when  it  is  closed. 


OPEN-CUT  MINING  163 

3.  Unskilled  labor  may  be  largely  employed. 

4.  May  serve  to  furnish  means  to  carry  on  development. 

5.  Removal  of  overburden  is  expensive,  so  cover  should 
be  thin. 

The  disadvantages  of  the  method  are: 

1.  Cost  of  mining  is  comparatively  high. 

2.  Operations  limited  to  small  outputs. 

3.  Owing  to  the  number  of  men  employed  the  method 
is  more  subject  to  interference  through  labor  trouble. 

SURFACE  MINING  BY  SCRAPERS 

The  use  of  scrapers  naturally  follows  hand  work  in  excava- 
tion, being  applied  to  operations  of  considerably  greater 
extent,  but  is  limited  to  earthy  and  moderately  soft  mate- 
rials. Drag  scrapers  are  extensively  employed  in  small-scale 
stripping  operations,  where  the  formations  overlying  coal 
beds  or  other  valuable  materials  consist  of  earth,  clays, 
shales  or  other  material  readily  loosened  by  pick,  plow  or 
small  charges  of  powder.  The  work  of  stripping  off  the 
overburden  is  usually  begun  at  the  point  where  it  is  the 
thinnest,  which  is  on  or  next  to  the  outcrop.  Outcrops 
usually  occur  on  hillsides,  on  the  banks  of  streams,  etc., 
where  the  materials  excavated  can  readily  be  disposed  of  at 
a  lower  level. 

Strip-pits  formed  by  scrapers  are  45  to  60  feet  wide  and 
vary  in  length  from  125  to  200  feet.  Larger  sized  pits 
cannot  be  worked  to  advantage  unless  wheeled  scrapers  are 
employed,  owing  to  too  much  time  being  lost  in  taking  and 
discharging  the  relatively  small  loads.  Thickness  of  cover 


164 


ORE  MINING   METHODS 


up  to  8  and  12  feet  can  be  removed  quickly  and  cheaply, 
while  banks  of  16  even  up  to  25  feet  are  occasionally  worked. 
It  is  doubtful  whether  it  pays  under  ordinary  circumstances 
to  strip  an  overburden  exceeding  16  feet  in  thickness;  how- 
ever, all  depends  upon  the  character  and  amount  of  the 


Fig.  56.— Stripping  Coal  by  Scrapers. 

material  being  stripped.  A  thick  stratum  of  coal  of  good 
quality,  a  good  bed  of  phosphate  rock,  gypsum  or  soft-iron 
ore  may  warrant  extensive  stripping  operations,  but  if  of 
considerable  lateral  extent,  more  economical  methods  should 
be  resorted  to  in  preparing  for  its  extraction. 

Stripping  operations  as  employed  in  uncovering  a  4O-inch 
coal  stratum  are  shown  in  Fig.  56.    The  width  and  length 


OPEN-CUT  MINING  165 

of  the  pit  are  shown  to  good  advantage,  also  the  sloping 
ends  or  entrances  to  the  pit,  a  wagon  road  being  cut  to 
lower  grade  at  the  far  end  into  the  pit  to  admit  wagons  by 
which  the  coal  is  hauled  out.  The  waste  or  waste-bank  is 
shown  to  the  left.  The  coal  having  been  removed,  the 
resulting  excavation  serves  as  a  receptacle  for  the  new 
waste-bank  formed  by  opening  up  another  pit  to  one  side 
of  the  previous  one. 

Water  when  it  occurs  in  considerable  quantities  is  one  of 
the  most  serious  problems  to  be  dealt  with  in  stripping,  as 
natural  drainage  cannot  always  be  effected.  Steam  pumps 
are  employed  in  the  larger-scale  work,  while  endless-belt 
pumps  driven  by  horse  power  are  commonly  used  in  freeing 
small  pits  of  excess  of  water.  A  belt  pump  is  shown  upon 
the  bank  to  the  right  of  the  pit,  Fig.  56. 

The  size,  both  width  and  length,  of  stripping  pits  may  be 
materially  increased  by  the  use  of  wheeled  scrapers,  which 
take  larger  loads  and  can  travel  greater  distances  to  the 
waste-bank  with  less  loss  of  time  than  can  the  drag  scrapes. 

Surface  work  with  scrapers  is  especially  applicable  to  de- 
posits of  large  lateral  extent  and  therefore  to  bedded  deposits. 
In  fact  the  method  is  practically  limited  to  stripping  opera- 
tions, as  in  coal,  phosphate  and  gypsum  mining. 

The  advantages  of  scraper  work  are : 

1.  Little  equipment  needed  besides  scrapers  and  plows. 

2.  Small  force  required. 

3.  Capacity  moderately  large. 

4.  Cost  of  mining  comparatively  low. 

5.  Unskilled  labor  may  be  employed. 


1 66  ORE   MINING  METHODS 

The  disadvantages  of  the  method  are: 

1.  Overburdens  exceeding  16  to  18  feet  cannot  be  econo- 
mically removed  unless  the  waste  can  be  stored  close  at 
hand. 

2.  Wear  of  scrapers  excessive. 

OPEN-CUT  MINING  BY  STEAM  SHOVEL 

The  advent  of  the  steam  shovel  into  mining  operations 
has  meant  much  to  the  industry,  and  it  is  largely  due  to  its 
extensive  employment  that  the  cost  of  mining  of  iron  ores 
has  been  reduced  to  an  amazingly  low  figure.  Probably 
the  most  extensive  field  of  operation  for  steam  shovels  is  in 
the  large  open-cut  iron  mines  of  Michigan  and  Minnesota, 
although  very  extensive  steam-shovel  work  is  being  done  in 
the  Bingham  Canyon  copper  mines,  similar  mines  at  Ely, 
Nevada,  and  in  the  Granby  mines,  British  Columbia.  (See 

Fig.  570 

Prior  to  the  application  of  steam-shovel  work  to  the  min- 
ing of  ore  the  overburden  must  be  removed.  This  is  done 
by  steam  shovels,  the  barren  material  being  loaded  into 
railroad  cars  or  other  cars  of  several  tons'  capacity.  When 
removed  by  small  cars  they  are  usually  transferred  to  the 
waste-bank  by  an  engine  plane  or  some  form  of  rope  haulage. 
An  overburden  ranging  up  to  40  feet  or  more  in  thickness 
is  not  uncommon,  and  while  greater  thicknesses  might  be 
removed  without  reaching  a  prohibitive  figure  from  the 
standpoint  of  costs,  yet  it  means  that  the  underlying  body 
of  ore  must  be  both  thick  and  of  high  grade.  The  thickness 
of  cover  considered  permissible  to  remove  depends  largely 


OPEN-CUT  MINING 


167 


upon  its  character,  i.e.y  if  soft  or  easily  broken  the  maximum 
economic  thickness  may  be  taken,  while  hard  stratified 
formations  may  reduce  the  thickness  to  a  few  feet  and  may 
even  preclude  the  employment  of  surface  methods  alto- 
gether. The  iron  deposits  of  the  Lake  Superior  region  are 
covered  with  glacial  drift  which  is  easily  and  cheaply  re- 
moved; considerable  thicknesses  extending  over  many  acres 


6900 


BOSTON 

CONSOLIDATED 


*  <*  <^UTAH^COPPER  COMPANY  *  " 

"^<l*<\ « *  *  ******  * 


Fig.  57.  —  Section  across  Bingham  Canyon,  showing  Beginning  of  Steam- 
Shovel  Work  in  Stripping  Capping. 

are  systematically  stripped  off  and  hauled  from  the  site  of 
the  mine.  (For  work  in  Alabama  mines  see  Fig.  58,  p.  170.) 
There  are  three  general  methods  of  steam-shovel  work; 
which  will  be  employed  in  a  given  case  depends  upon  exist- 
ing conditions.  Lateral  extent,  elevation  with  respect  to 
the  surrounding  country,  amount  of  overburden,  and  depth 
to  which  the  deposit  extends  are  controlling  factors  in  the 


1 68  ORE  MINING  METHODS 

choice  of  methods  of  procedure  in  opening  up  and  working 
a  steam-shovel-operated  mine.  The  deposit  having  been 
definitely  located  by  test  pits  and  drill  holes  and  the  over- 
burden removed  from  the  area  in  which  mining  is  to  begin, 
the  work  of  opening  up  the  deposit  is  begun.  The  initial 
opening  may  be  in  the  form  of  a  cut  extending  through  the 
middle  of  the  deposit  or  along  one  side,  whichever  seems 
more  advisable  from  the  standpoint  of  maintaining  grades. 
If  an  opening  is  made  through  the  middle  of  the  deposit,  the 
work  of  cutting  out  the  ore  may  be  carried  on  laterally  in 
both  directions,  while  if  begun  on  one  side  it  will  have  to  pro- 
ceed in  one  direction  only.  Again,  and  in  a  similar  manner, 
a  deposit  may  be  opened  by  running  a  spiral  cut  partly 
in  the  ore-body  and  working  radially  inward  and  outward, 
or  the  deposit  may  be  attacked  and  encircled  by  the  cut, 
the  removal  of  the  ore  proceeding  inward  to  the  center  of 
the  deposit.  In  either  case,  where  a  spiral  cut  is  made,  the 
ultimate  form  of  the  deposit  is  a  pit,  the  lowest  portion 
being  reached  by  spiral  tracks  upon  which  the  steam  shovels 
and  ore  trains  operate.  The  coils  of  the  spiral  are  con- 
stantly widening  as  slices  are  removed  from  the  faces  of  the 
banks  or  terraces.  Care  must  be  taken  to  maintain  the 
proper  grade  on  the  spiral. 

Ore?  specially  suited  to  steam-shovel  work  should  be  soft  or 
at  least  easily  broken  up  by  small  charges  of  powder  which 
are  placed  in  advance  of  the  steam  shovel  work.  The 
shovel  stands  next  to  the  bank  from  which  it  takes  its  load, 
removing  a  slice  or  cut  of  6  or  8  feet  in  width  and  depositing 
the  excavated  ore  in  the  railroad  cars  standing  on  the  track  to 


OPEN-CUT  MINING  169 

one  side  of  the  shovel.  A  cut  having  been  made  sufficiently 
wide  for  four  lines  of  track  or,  if  work  is  done  on  both  sides 
of  the  cut,  wide  enough  for  six  lines  of  track,  another  cut 
will  be  opened  to  one  side  in  the  former  case,  or  in  the 
middle  of  the  cut  in  the  latter  case.  A  series  of  levels  is 
thus  formed,  giving  the  excavation  a  stepped  or  terraced 
form.  A  large  number  of  points  of  attack  are  thus  made 
possible,  increasing  the  capacity  of  the  mine  and  reduc- 
ing the  cost  of  mining  by  getting  the  most  out  of  the 
equipment. 

Still  another  method  of  steam-shovel  work  is  that  in  which 
the  shovel  operates  at  the  bottom  of  a  deep  pit  where  it  is 
employed  in  excavating  and  in  loading  mine  cars,  which  are 
run  to  the  foot  of  a  shaft  and  hoisted  to  the  surface  as  in 
underground  work.  In  this  method  the  steam  shovel  is  as- 
sembled at  the  bottom  of  the  pit,  its  chief  function  being  the 
loading  of  cars.  Hard  ores  may  be  blasted  down  and  then 
loaded  into  the  cars  by  the  steam  shovel.  While  this  method 
is  rather  limited  in  its  application,  yet  it  serves  a  useful  pur- 
pose under  certain  conditions  of  ore  occurrences  necessitat- 
ing special  methods  of  working, 

A  not  unimportant  use  to  which  the  steam  shovel  has  been 
put  is  that  of  loading  ore  from  stock  piles  where  it  is  stored 
during  the  winter  months,  traffic  being  closed.  Practically 
all  underground  operations  are  continued  throughout  the 
winter,  the  ore  raised  being  stored  in  the  stock  piles.  Fur- 
ther, it  is  not  unusual  for  ore  to  be  excavated  and  piled  up 
in  the  open-cuts  by  the  steam  shovels,  where  it  remains 
frozen  until  spring,  when  it  is  loaded  in  the  railroad  cars  by 


170 


ORE  MINING   METHODS 


OPEN-CUT  TV1INING  171 

steam  shovels  in  the  same  way  as  are  the  stock  piles  of 
hand-mined  ore. 

Steam  shovels  are  also  occasionally  employed  in  excavat-. 
ing  materials  below  water  level,  as  in  mining  phosphates  in 
the  Southern  states.  In  such  work  it  is  necessary  to  operate 
the  shovel  on  solid  ground,  which  is  accomplished  by  strip- 
ping the  deposit  and  then  employing  a  steam  shovel  with  a 
'  broken '  boom,  i.e.,  a  boom  in  the  shape  of  an  inverted  V, 
the  dipper  being  supported  by  the  outer  and  downward 
sloping  part.  Further,  the  dipper  faces  toward  the  shovel 
and  takes  its  load  inward  rather  than  outward.  By  this 
arrangement  the  shovel  is  required  to  operate  backward, 
but  always  upon  the  solid,  unexcavated  bed  of  phosphates. 
The  dipper  takes  its  load  partially  under  water,  but  dis- 
charges it  into  cars  standing  on  a  track  to  one  side  of  that 
upon  which  the  shovel  operates  and  usually  at  a  high  level. 

The  combination  of  steam-shovel  mining  with  improved 
methods  of  extraction  of  metals  from  low-grade  ores  will 
make  possible  the  opening  up  and  successful  working  of 
many  large  deposits  which  are  at  present  unworkable. 
The  steam  shovel  has  already  in  many  cases  been  an  im- 
portant factor  in  reducing  the  cost  of  mining  cheap  ores  and 
has  thus  made  a  market  for  them. 

The  use  of  steam  shovels  is  applicable  to  massive  deposits 
of  a  wide  range  in  hardness,  although  those  ores  that  break 
up  readily  are  the  best  suited  to  the  work. 

The  advantages  of  steam-shovel  work  are: 

1.  Large  outputs. 

2.  Low  mining  costs. 


172  ORE   MINING   METHODS 

3.  Railroad  cars  may  be  loaded  directly,  thus  reducing 
cost  of  handling. 

4.  Thick  overburdens  can  be  removed  economically. 
The  disadvantages  of  the  method  are: 

1.  Expenditure  for  equipment  rather  high. 

2.  Rate  of  depreciation  high. 

3.  Skilled  labor  required  for  handling  shovels. 

THE  MILLING  METHOD 

That  particular  application  of  open-cut  mining  known  as 
the  milling  method  is  in  reality  a  combination  of  open-cut 
and  underground  work,  or,  more  strictly  speaking,  mining  in 
an  open-cut  and  handling  the  ore  underground.  Owing  to 
the  successful  application  of  the  milling  method  as  origi- 
nally employed  in  surface  work,  it  is  now  being  extended  to 
underground  work,  where  it  is  also  meeting  with  marked 
success,  in  certain  instances  at  least. 

The  milling  method  is  underhand  stoping  applied  to 
large  deposits,  the  work  of  cutting  out  the  ore  being  con- 
fined to  limited  areas  around  the  mouths  of  raises  or  winzes. 
In  developing  a  deposit  to  be  worked  by  the  milling  method 
it  is  essential  that  the  haulage-ways  on  the  respective  levels 
be  so  arranged  as  to  facilitate  the  handling  of  large  quan- 
tities of  ore,  as  the  milling  method  is  productive  of  large 
tonnage.  This  can  best  be  done  by  so  arranging  the  haul- 
age-ways that  the  going  and  returning  ways  are  separate, 
thus  eliminating  the  interference  of  loaded  and  empty  cars. 
Parallel,  elliptical  or  roughly  circular  systems  of  haulage- 
ways,  connected  by  cross-cuts  at  frequent  intervals  to  facili- 


OPEN-CUT  MINING  173 

tate  the  movement  of  cars,  provide  ample  opportunity  for  the 
handling  of  both  loaded  and  empty  cars.  Such  development 
work  is  done  on  each  level,  but  not  necessarily  completed, 
except  on  the  upper  level,  until  the  surface  workings  have 
reached  and  destroyed  the  haulage-ways  on  that  level, 
when  a  similar  arrangement  of  ways  should  be  in  readiness 
for  handling  the  ore  on  the  level  below,  and  so  on,  level  by 
level,  as  the  work  progresses  downward.  (See  Fig.  59.) 

The  development  work  on  a  level  having  been  com- 
pleted, raises  are  put  up  along  the  line  of  the  haulage- 
ways  at  intervals  of  50  to  75  feet  or  more.  The  barren 
material  forming  a  covering  to  the  ore-body  should  be 
removed  before  the  raises  break  through  to  the  surface. 
Chutes  for  the  control  of  the  ore  and  the  loading  of  cars  are 
placed  at  the  foot  of  each  raise,  and  when  so  equipped 
the  work  of  breaking  the  ore  may  be  begun.  Drills  are 
mounted  on  tripods  at  the  edge  of  the  raises,  and  the  ore 
broken  by  the  charges  so  placed  falls  by  gravity  into 
the  raises,  from  which  it  is  drawn  into  cars  and  sent  to  the 
surface.  Pits  are  soon  formed  about  the  mouths  of  the 
respective  raises,  which  as  they  increase  in  size  provide 
more  room  for  other  groups  of  drillers.  Ultimately  the 
pits  formed  along  the  line  of  a  haulage-way  run  together, 
as  do  those  of  different  lines  of  haulage,  thus  forming  a 
large  pit  the  bottom  of  which  is  composed  of  a  number  of 
inverted  conical  openings  connected  by  raises  with  the 
underground  haulage  system.  It  is  evident  that  after  the 
pits  have  coalesced  the  rims  of  the  raises  will  have  re- 
solved themselves  into  ridges  standing  between  the  pits, 


174  ORE  MINING  METHODS 

upon  which  ridges  the  mounting  of  drills  is  practically  im- 
possible. 

Further  breaking  of  ore  must  then  be  done  in  one  of 
two  ways,  namely:  the  drilling  is  done  by  hand  drillers 
operating  miscellaneously  on  the  sloping  surface  of  the  pits 
or  by  systematic  work,  beginning  at  the  bottom  of  the 
funnel-shaped  pits  and  proceeding  upward.  Sections  rang- 
ing from  a  few  up  to  10  and  12  feet  in  thickness  are  thus 
removed  from  the  bottom  to  the  top  of  the  pits,  the  drills 
being  returned  to  the  bottom  after  each  section  is  com- 
pleted, when  work  upon  another  section  is  begun.  The 
work  of  breaking  the  ore  may  then  be  accomplished 
by  either  underhand  or  overhand  stoping,  the  former  at 
the  beginning  of  the  operations,  the  latter  after  the 
milling  pits  have  run  together  forming  one  large  open- 
cut.  As  many  as  twenty  milling  pits  may  be  worked 
together,  but  probably  ten  or  thereabouts  is  a  more  usual 
number. 

Those  ores  that  break  up  into  moderately  small  pieces 
are  best  suited  to  the  milling  method,  although  fairly  hard 
ores  are  worked  satisfactorily.  Care  must  be  taken  to 
insure  against  falls  of  rock  or  ore  while  the  laborers  are  at 
work  in  the  pits,  which  can  only  be  done  by  barring  down 
all  loose  rock  and  even  employing  small  charges  of  pow- 
der to  remove  dangerous  portions  of  the  walls. 

Steam  shovels  are  occasionally  employed  in  conjunction 
with  the  milling  method,  being  used  to  excavate  the  ore 
and  dump  it  into  the  milling  pits.  Owing  to  the  limited 
space  for  trackage  and  the  difficulty  experienced  in  properly 


OPEN-CUT  MINING  175 

arranging  and  maintaining  the  working  of  the  steam  shovels 
about  the  pits,  this  particular  phase  of  the  milling  method 
is  comparatively  little  used. 

Glory-hole  mining  is  the  milling  method  after  it  has  been 
fully  developed,  i.e.,  after  the  pits  formed  by  breaking  ore 
round  the  mouths  of  the  raises  have  run  together  and 
by  continued  work  have  reached  considerable  depth,  thus 
forming  a  large  and  deep  excavation.  Glory-hole  mining 
is  employed  in  practically  all  mines  where  large  ore-bodies 
occur  at  the  surface,  the  more  superficial  portions  being 
worked  by  open-cuts  operated  by  hand  and  in  many  cases 
resembling  quarrying  methods.  After  a  certain  depth  has 
been  reached  tunnels  may  be  employed  which  connect  with 
a  shaft  or  with  the  surface  at  lower  levels.  In  the  mean- 
while the  lode  will  have  been  developed  in  depth  and  raises 
put  up  which  finally  connect  with  the  bottom  of  the  open- 
cut,  when  the  work  of  handling  the  ore  is  transferred  from 
the  tunnel  levels  to  the  main  levels  of  the  mine  by  way  of 
the  mill  holes.  Owing  to  the  likelihood  of  large  masses  of 
rock  and  ore  falling  into  the  mill  holes  and  choking  them, 
it  is  common  practice  to  provide  a  grizzly  of  logs  at  the 
top  of  the  raises,  thus  separating  out  the  boulders,  which 
are  reduced  to  the  proper  size  to  pass  the  grizzlies  by  sledge 
or  bulldozing,  i.e.,  by  the  use  of  small  charges  of  powder. 
Further,  in  order  to  prevent,  or  reduce  to  a  minimum,  the 
choking  of  the  mill  holes  it  is  often  necessary  to  change  the 
direction  of  the  holes.  Also  in  order  to  reduce  or  entirely 
eliminate  the  weight  of  the  column  of  broken  ore  standing 
in  the  mill  holes,  the  holes  may  be  offset  to  one  side  of  the 


i76 


ORE  MINING  METHODS 


en 

I 
a 


t 

O 


bp 

£ 


OPEN-CUT  MINING  177 

haulage-way  or  tunnel  below,  thus  requiring  less  support  to 
maintain  them. 

While  many  ore-bodies  are  of  fairly  uniform  value  through- 
out, there  are  others  in  which  the  values  are  very  spotted, 
the  workable  portions  coming  and  going  in  a  very  irregular 
manner.  It  is  evident,  then,  that  where  deposits  of  variable 
mineral  content  are  worked  by  the  milling  method,  especially 
in  the  large  open-cuts  where  little  or  no  discrimination  can 
be  made  between  ore  and  waste  in  breaking  down  the  walls, 
all  material  entering  the  mill  holes  must  be  taken  care  of, 
which  is  usually  done  by  sending  the  waste  to  empty  or  work- 
ing stopes  as  filling,  while  the  ore  is  diverted  to  the  loading 
chutes  for  cars.  This  is  made  possible  by  employing  a 
number  of  mill  holes  so  arranged  that  accumulations  of  ore 
or  waste  may  be  drawn  off  alternately  through  one  or  more 
of  the  holes.  It  is  claimed  that  it  is  not  uncommon  for  two 
men  to  loosen  and  mill  as  much  as  300  and  400  tons  of  ore 
per  day. 

The  name  "  glory-hole "  probably  came  to  be  applied  to 
the  large  open-cuts  because  of  the  large  number  of  deaths  of 
laborers  working  in  and  about  them  —  the  victims  of  falls 
were  spoken  of  as  having  gone  to  Glory. 

As  previously  mentioned,  the  milling  method  of  mining  is 
occasionally  employed  underground,  when  it  is  often  referred 
to  as  underground  glory-hole  method.  Where  the  overburden 
is  too  thick  for  economical  removal  and  the  deposit  warrants 
its  use  the  milling  method  may  be  employed,  the  raises  being 
put  up  to  or  close  to  the  top  of  the  ore-body  and  the  work 
of  breaking  ore  begun  by  working  laterally  and  downward. 


178  ORE  MINING  METHODS 

Large  roughly  circular  stopes  or  rooms  are  thus  formed,  in 
the  centers  of  which  are  the  mill  holes  or  raises.  The  over- 
burden is  supported  either  by  timbers  placed  across  the  top 
of  the  stope,  usually  in  A-form,  or,  if  the  stope  is  not  too  wide 
and  the  ore  is  sufficiently  strong  to  stand,  a  back  of  ore 
several  feet  in  thickness  may  be  left,  being  formed  into  an 
arch,  thus  doing  away  with  timber  supports.  Stopes  of 
one  hundred  or  more  feet  in  height  may  be  worked  in  this 
manner,  but  a  large  part  of  the  ore-body  is  left  standing 
between  the  stopes.  If  the  mineral  is  cheap,  as  rock  salt,  this 
might  be  permitted,  otherwise  some  other  method  of  mining 
should  be  employed.  A  similar  method  has  been  employed 
in  the  iron  mines  of  the  Lake  Superior  region,  but  had  to 
be  supplemented  by  some  other  method,  which  is  somewhat 
difficult  to  do  owing  to  the  large  open  stopes,  the  collapse 
of  which  must  not  only  be  expected  but  provided  for. 

Pillars  left  in  the  preliminary  working  of  a  deposit  may 
later  be  removed,  even  when  the  stopes  have  been  filled  or 
have  caved,  by  putting  up  raises  to  the  pillars  and  cutting 
them  out  by  overhand  stoping,  or  the  raises  may  be  run 
through  the  pillars,  and  by  careful  timbering  the  pillars  may 
be  removed  by  underhand  stoping.  In  a  similar  manner 
the  filling  in  stopes,  that  was  formerly  considered  too  poor 
to  work  with  profit,  but  by  improved  processes  has  been 
rendered  profitable  to  treat,  may  be  drawn  off  by  putting  up 
raises  and  tapping  the  stopes.  Great  care  must  be  taken  in 
all  of  this  work  in  order  to  control  the  caving  that  is  almost 
sure  to  follow  the  removal  of  large  quantities  of  material 
in  comparatively  short  periods  and  in  limited  areas. 


OPEN-CUT  MINING  179 

The  milling  method  is  probably  most  extensively  em- 
ployed in  the  Michigan  and  Minnesota  iron  fields,  where  it 
is  used  both  as  a  surface  or  open-cut  method  and  under- 
ground. Similar  methods  are  in  use  at  the  Alaska-Tread- 
well  mines,  Douglas  Island,  Alaska;  at  the  Homestake 
mines,  Lead,  South  Dakota;  in  the  gold  mines  at  Goldfield, 
Nevada;  at  the  Comstock  Lode,  Virginia  City,  Nevada;  in 
the  copper  mines  of  Bingham  Canyon,  Utah;  in  the  Yellow 
Aster  Mine,  Randsburg,  California;  in  the  Big  Indian  Mine, 
Helena,  Montana;  in  the  Granby  mines,  Phoenix,  British 
Columbia,  and  at  numerous  other  mines. 

The  milling  method  of  mining  is  applicable  to  large  bodies 
of  ore  either  in  veins  or  masses,  and  to  wide  ranges  in  char- 
acter of  ore.  The  method  is  elastic,  as  it  is  employed  in 
both  surface  and  underground  work. 

The  advantages  of  the  milling  method  are : 

1.  Large  outputs  per  man. 

2.  Low  mining  costs. 

3.  Much  waste  material  may  be  obtained  for  filling,  which 
is  important  if  other  methods  of  mining  are  operated  in 
conjunction  with  the  milling  method. 

4.  There  is  a  minimum  amount  of  handling  of  ore. 

5.  When  working  ground  previously  mined  in  which  con- 
siderable timber  was  used,  much  of  the  timber  can  be  picked 
from  the  ore  and  reused. 

The  disadvantages  of  the  method  are: 

i.  When  employed  as  a  surface  method  of  working, 
the  ore-body  must  extend  close  to  the  surface  to  be 
stripped. 


l8o  ORE  MINING  METHODS 

2.  Mill  holes  choke,  especially  with  ores  of  certain  char- 
acter; ores  breaking  moderately  fine  and  granular  in  form 
without  clay  are  preferable. 

3.  Rain  and  snow  interfere  with  work  on  the  sloping 
sides  of  the  pits. 

4.  Considerable  danger  from  falls  of  men  and  rocks  and 
flying  rock  from  blasts. 

5.  When  carried  on  underground  there  is  considerable 
danger  of  caves  which  may  extend  into  the  workings. 

6.  Little  opportunity  to  sort  ore  from  waste. 
Generally  considered,  surface  or  open-cut  methods  are 

applicable  to  the  outcrops  of  large  veins  and  massive  de- 
posits occurring  at  or  within  a  few  feet  of  the  surface. 
Practically  all  kinds  of  minerals  and  ores  as  well  as  non- 
metalliferous  materials  are,  when  possible,  mined  by  open- 
cuts.  Quarries  of  stone,  slates,  etc.,  are  to  all  intents  and 
purposes  open-cut  mining  operations  and  may  be  classed  as 
open-cut  mining. 

The  advantages  of  open-cut  mining  are: 

1.  Work  can  be  done  on  a  large  scale. 

2.  Mining  cost  is  low. 

3.  Lighting  workings  is  eliminated  or  materially  lessened. 

4.  No  timber  is  required. 

5.  Sorting  can  be  done  to  advantage. 

6.  Practically  no  danger  from  fires,  gases,  etc. 
The  disadvantages  of  open-cut  work  are : 

1.  Cost  of  real  estate  for  both  the  open-cut  and  storage 
of  waste  is  a  large  item. 

2.  The  depth  to  which  the  strictly  open-cut  wTork  can  be 


OPEN-CUT   MINING  181 

carried  is  limited,  although  with  the  milling  method  great 
depths  are  worked. 

3.  The  cost  increases  greatly  with  depth,  unless  connec- 
tion is  made  with  the  underground  workings  as  in  glory-hole 
work. 

4.  Danger  of  falls  of  rock  and  men. 

5.  Danger  of  inundations. 

6.  Inconvenience  of  working  in  stormy  weather. 

7.  Proper  slopes  must  be   given   to   the    sides  of    the 
open-cuts   to  prevent  walls   from   caving  —  a   slope   of   i 
to  ij  for  hard  formations  and  i  to  3  for  clay  is  commonly 
given. 

The  comparative  advantages  and  disadvantages  of  the 
various  methods  of  open-cut  work  are  as  follows: 

1.  The  outputs  of  the  milling  method  and  steam-shovel 
work  are  much  greater  per  man  than  by  hand  or  scraper 
work,  and  by  scraper  than  by  hand  work. 

2.  The  cost  of  mining  per  ton  is  much  less  with  the  milling 
method  and  steam  shovel  than  with  hand  and  scraper  work, 
while  scraper  work  is  cheaper  than  hand  work,  and  steam- 
shovel  work  is  cheaper  than  by  milling. 

3.  The  milling  method  can  be  used  to  advantage  in  de- 
posits too  small  for  steam  shovels  to  operate  upon. 

4.  Fewer  laborers  are  required  in  scraper  than  in  hand 
work,   and  in  steam-shovel   than  in   the   milling   method, 
but  more  skilled  labor   is   required   in   steam-shovel   and 
milling. 

5.  Less  danger  of  accidents  in  hand,  scraper  and  steam- 


182  ORE  MINING  METHODS 

shovel  work  than  in  the  milling  method,  and  more  in  hand 
and  steam-shovel  work  than  in  scraper  work. 

6.  Ores  may  be  sorted  to  better  advantage  by  hand, 
scraper  and  steam-shovel  work  than  in  the  milling  method, 
and  better  in  hand  and  scraper  than  with  steam-shovel 
work. 


CHAPTER  VI 
COST    OF    STOPING 

INTRODUCTION 

As  stoping  is  the  fundamental  operation  in  metal-mining 
its  cost  constitutes  the  largest  item  in  the  extraction  of 
ore.  The  cost  of  stoping  s  dependent  upon  a  number  of 
more  or  less  general  considerations,  such  as  period  of  opera- 
tion, value  of  ore,  organization  of  working  force,  extent  of 
operation,  transportation  facilities,  etc.  A  number  of  these 
factors  are  interdependent,  as  time  work  has  been  carried 
on,  extent  of  operation,  organization,  etc.;  the  scale  of 
operation  and  organization  naturally  requires  time  for  growth 
and  perfecting  The  same  is  true  of  transportation  facili- 
ties, but  probably  to  a  less  degree.  Increased  output  made 
possible  by  efficient  equ'pment  and  organization  is  without 
doubt  the  most  important  factor  in  reduction  of  costs, 
which  is  true  not  only  of  the  breaking  of  ore  but  of  every 
other  operation  both  above  and  below  ground.  Hard  times 
also  act  to  reduce  cost  of  working,  but  like  the  cause  that 
produces  them,  stringency  in  the  money  market,  the  condi- 
tions are  abnormal  and  are  to  be  considered  as  cause  of  tem- 
porary variations  only  and  not  as  constantly  acting  factors. 

Speaking  more  specifically,  the  cost  of  breaking  ore  is 
influenced  by  variations  of  value  of  ore  with  depth,  hardness 

of  ore  and  gangue  materials,  presence  of  water,  cost  of  labor 

183 


1 84  ORE  MINING  METHODS 

and  supplies,  etc.  Variations  in  width  of  deposits,  the  min- 
eral content  remaining  the  same  per  foot  in  depth,  means  the 
handling  of  more  or  less  material  with  the  same  ultimate  re- 
turn, and  may  be  a  potent  factor  in  increasing  cost  of  work- 
ing, as  it  necessitates  the  breaking  of  much  wall-rock,  as  in 
resuing.  The  hardness  of  the  ore  may  also  vary  considerably 
with  depth  and  if  coincident  with  reduced  mineral  content 
may  result  in  a  very  material  increase  in  cost  of  stoping. 

The  stability  of  both  vein-content  and  wall-rock,  i.e.,  the 
ability  to  stand  unsupported  in  moderate  sized  stopes,  is 
probably  of  equal  importance  with  hardness  of  the  mineral 
bearing  and  non-mineral  bearing  formations.  Weak  and 
unstable  formations  involve  the  element  of  support,  which  in 
extreme  cases  may  increase  the  cost  of  working  to  a  prohibi- 
tive figure.  By  carefully  arching  the  backs  of  the  stopes, 
stable  formations  may  be  made  to  stand  otherwise  unsup- 
ported in  stopes  50  feet  or  more  in  width;  the  large  open 
stopes  of  the  Homestake  mines  of  South  Dakota,  and  of  the 
Alaska-Treadwell  mines,  Douglas  Island,  Alaska,  are  good 
illustrations  of  such  conditions.  On  the  other  hand  weak  and 
unstable  formations  may  be  worked  at  moderately  low  costs 
by  the  employment  of  filling  methods.  As  the  conditions 
existing  in  the  majority  of  the  metal  mines  of  the  United 
States  are  such  as  to  necessitate  support,  it  is  evident  that 
the  cost  of  support  may  enter  into  the  expense  of  working 
and  often,  as  in  square-set  mining,  constitutes  an  important 
item  in  such  calculations. 

The  character  of  the  ore  is  of  importance,  for  if  the  whole 
vein-content  is  uniform  in  value,  the  method  of  working  the 


COST  OF  STOPING  185 

deposit  will  differ  materially  from  the  case  where  the  values 
are  scattered,  occurring  possibly  in  thin  stringers  or  in 
bunches.  In  the  former  case  the  value  can  be  depended 
upon  and  will  vary  between  moderately  narrow  limits;  in 
the  latter  case  much  barren  material  will  have  to  be  mined 
thus  necessitating  considerable  sorting.  Further,  in  the 
former  case  we  may  have  a  concentrating  ore  from  which 
the  waste  may  be  largely  eliminated,  in  the  latter  case  a 
smelting  ore  may  be  the  result;  in  either  case  the  subsequent 
metallurgical  treatment  is  really  the  determining  factor  in 
the  economical  working  of  the  deposit.  While  it  costs  as 
much  to  break  waste  as  to  break  ore,  yet  the  tonnage  costs 
are  usually  charged  to  ore  alone,  which  is  an  important  con- 
sideration in  figuring  costs. 

The  presence  of  water  in  considerable  quantities  does  not 
directly  influence  the  cost  of  breaking  ore;  however,  there 
are  numerous  instances  where  excessive  quantities  of  water 
are  encountered,  even  in  certain  portions  of  otherwise  mod- 
erately dry  districts,  and  in  such  cases  the  cost  of  breaking 
ore  may  run  up  to  an  abnormally  high  figure.  Aside  from 
the  inconvenience  of  working  at  a  stope  face  flooded  with 
water  or  in  a  constant  downpour  from  the  roof,  the  presence 
of  large  quantities  of  water  materially  increases  the  peril 
of  working,  increasing  the  number  of  falls  both  by  prevent- 
ing adequate  inspection  and  by  the  tendency  to  force  off 
the  fractured  rock  and  ore  by  hydraulic  pressure.  Falls  of 
rock  may  be  largely  increased  by  the  action  of  water  under 
pressure  acting  in  crevices,  fault  planes  and  slips,  especially 
when  an  attempt  is  made  to  check  the  flow  by  wedging  and 


1 86  ORE  MINING  METHODS 

pumping  in  cement,  clay,  sawdust,  etc.,  as  was  done  in  the 
Central  Mine  of  the  Federal  Lead  Company  at  Flat  River, 
Missouri. 

While  the  wages  paid  in  the  various  metal  mining  districts 
of  the  United  States  vary  considerably,  yet  the  actual  differ- 
ence in  cost  for  work  done  is  relatively  slight.  The  efficiency 
of  the  labor  depends  directly  upon  the  wage  paid,  although 
there  are  possible  exceptions,  as  under  certain  conditions 
of  labor,  location,  etc.  The  operator  then  gets  a  return 
for  his  labor  expenditure  in  proportion  to  the  amount  paid. 

The  cost  of  supplies,  such  as  fuel  for  power  purposes, 
timber  for  support,  and  tools,  steel,  explosives,  etc.,  for 
breaking  ground,  while  it  varies  considerably  in  various 
localities,  probably  does  not,  as  Finlay  has  shown,  even  with 
a  variation  of  50  per  cent  in  the  price,  produce  a  difference 
of  over  10  per  cent  in  total  current  mining  costs. 

Other  conditions  having  an  indirect  bearing  upon  the  cost 
of  working  and  especially  stoping  are :  abnormal  temperature 
of  the  mine  atmosphere;  presence  of  gases,  natural  or  arti- 
ficial; dust  resulting  from  operation  of  drills;  altitude,  etc. 
High  temperature  may  be  due  to  inherent  qualities  in  the 
deposit  worked  or  to  poor  and  inadequate  ventilation. 
Excessive  temperatures  such  as  are  experienced  in  the  mines 
of  the  Comstock  Lode  and  a  few  other  mines  in  the  United 
States  are  not  of  sufficiently  common  occurrence  to  warrant 
consideration  in  this  connection,  but  temperatures  of  75  to 
90  degrees  are  of  fairly  common  occurrence  and  are  to  be 
found  in  the  lower  levels  of  many  mines  in  this  country. 
The  deeper  mines  of  Keweenaw  Point,  Michigan;  of  the 


COST  OF  STOPING  187 

Butte  District,  Montana;  and  of  other  western  districts 
may  be  cited  as  illustrations  of  mines  having  temperatures 
above  the  normal.  The  reduced  efficiency  and  effectiveness 
of  the  labor  returns,  while  apparently  inconspicuous  and 
relatively  small  considered  by  individual  units,  are  in  reality 
of  much  importance  when  the  elements  of  time  and  numbers 
are  involved.  Considered  independently  of  other  conditions 
a  few  degrees  rise  in  temperature  does  not  in  the  long  run 
have  a  deleterious  effect  upon  the  efficiency  of  labor,  but 
when  combined  with  other  conditions,  such  as  vitiated  air 
resulting  from  the  presence  of  moisture,  mine  gases  and 
powder  smoke,  may  seriously  affect  the  health  of  the  miners 
and  decrease  the  effectiveness  of  their  labor. 

Altitude  has  a  twofold  influence  upon  labor  conditions  in 
that  it  affects  the  health  and  general  tone  of  the  individual  ef- 
fort, and  by  its  effect  upon  climatic  conditions  may  seriously 
curtail  the  extent  and  duration  of  the  operations.  Further, 
the  operations  may  be  limited  to  certain  seasons  by  no  other 
cause  than  the  possibility  of  transportation,  excessive  rain- 
fall and  deep  snowfall  limiting  the  operation  of  the  rail- 
roads. Limited  periods  of  operation  in  turn  affect  the 
labor  conditions,  requiring  high  wages  to  maintain  the  proper 
standard  of  efficiency. 

DETAILED  DISCUSSION  OF  COSTS  OF  STOPING 

The  principal  factors  influencing  costs  of  mining  ore  have 
been  indicated  in  the  preceding  pages,  and  particularly 
those  entering  more  or  less  directly  into  the  cost  of  break- 
ing ore  or  s toping.  When  an  attempt  is  made  to  investigate 


iS8  ORE  MINING  METHODS 

the  cost  of  any  one  single  operation,  as  stoping,  it  at  once 
becomes  obvious  that  there  are  many  difficulties  to  be 
encountered.  It  is  rarely  the  case  that  reliable  information 
can  be  secured  regarding  the  cost  of  distinctively  separate 
operations,  the  tendency  in  ordinary  mining  practice  and 
cost-keeping  being  to  group  certain  closely  related  expenses 
under  a  few  more  or  less  general  headings,  such  as  mining, 
milling,  and  smelting.  These  may  in  turn  be  subdivided 
into  other  more  specific  yet  generalized  headings,  as  in  the 
case  of  mining,  where  we  may  have  costs  of  development, 
stoping  and  handling  ore. 

While  the  cost  of  stoping  is  here  specifically  stated,  yet  a 
careful  differentiation  of  expenses  between  stoping,  timber- 
ing, handling  ore,  and  labor  and  supplies  is  rarely  attempted. 
The  cost  of  mining  as  usually  given  in  published  reports  of 
mining  operations  is  more  often  misleading  than  otherwise 
in  that  there  are  a  number  of  unknown  factors  involved,  the 
result  being  that  the  figures  are  of  little  or  no  value  even  for 
comparative  purposes. 

The  cost  of  breaking  ore  or  stoping  per  unit  amount,  as 
per  ton  or  cubic  yard,  fathom,  etc.,  when  shorn  of  all  super- 
fluous and  extraneous  charges  may  be  considered  as  made 
up  of  the  following  items: 

1.  Cost  of  labor. 

2.  Cost  of  supplies. 

3.  Cost  of  power. 

4.  Cost  of  lighting. 

5.  Cost  of  support  in  stopes. 

6.  Cost  of  handling  ore  in  stopes. 


COST  OF  STOPING  189 

The  first  four  items  given  above  are  costs  common  to 
stoping  operations,  largely  independent  of  local  conditions. 
The  two  last  mentioned  items  may  be  considered  as  special 
costs  in  that  they  involve  special  methods  of  working 
brought  about  by  local  conditions  and  character  of  deposit. 

The  wage-scale  of  a  district  is  indicative  of  both  the 
character  and  efficiency  of  the  labor.  A  difference  of  30 
cents  per  hour  (range  20  to  50  cents  in  the  United  States) 
may  be  and  is  usually  largely  due  to  the  quantity  and  quality 
of  labor  available.  In  this  connection  the  question  might 
properly  be  raised  as  to  what  constitutes  a  day's  work. 
Aside  from  the  element  of  time  or  hours  of  work,  as  deter- 
mined by  local  agreement  or  law,  by  far  the  most  important 
consideration  is  the  quality  of  the  work  done,  and  this  in 
turn,  as  has  been  indicated,  is  largely  dependent  upon  wages 
paid.  High  wages  attract  good  workmen  and  by  competi- 
tion the  poorer  element  is  eliminated.  Difference  in  length 
of  a  working  day  and  of  wages  per  day  is,  however,  more 
apparent  than  real;  the  result  being  ultimately  about  the 
same,  the  conditions  naturally  equalizing  themselves  in 
quantity  and  quality  of  work  done.  Further,  a  day's  work 
may  be  based  upon  time  or  work  done,  and  as  in  practically 
all  other  kinds  of  work  the  latter  has  been  found  to  be 
much  more  satisfactory,  as  it  encourages  competitive  effort, 
which  means  both  more  work  done  and  a  higher  class  of 
work. 

In  stoping  it  is  customary  to  pay  for  footage  drilled  or 
volume  of  ore  broken  down,  as  per  cubic  foot,  yard  or 
fathom,  or  the  unit  adopted  for  calculation  of  wages  earned 


I  QO  ORE  MINING  METHODS 

may  be  the  tonnage  extracted,  which  is  in  reality  figured 
on  the  basis  of  volume  The  unit  of  volume,  be  it  figured 
in  feet,  yards  or  fathoms,  or  tons,  is  that  commonly  chosen 
for  contract  work. 

The  cost  of  supplies  varies  with  the  district  and  is  depend- 
ent largely  upon  transportation  facilities,  quantity  con- 
sumed, character  of  labor,  etc.  The  quality  of  the  supplies 
and  the  useful  amount  of  work  gotten  out  of  them,  whether 
good  quality  or  poor,  is  also  comparable  with  labor  and 
depends  more  or  less  directly  upon  the  character  of  the  labor 
employed. 

The  cost  of  power  to  any  particular  operation  is  difficult 
to  determine,  as  only  a  part  and  often  a  comparatively  small 
part  is  consumed  in  the  particular  operation  under  considera- 
tion. In  the  case  of  stoping,  however,  the  proportionate 
amount  of  power  used  is  relatively  large  compared  with 
other  power  consuming  operat  ons  underground,  yet  while 
the  error  in  estimation  of  amount  to  be  charged  to  stoping 
may  be  small,  it  exists  nevertheless,  but  may  for  comparative 
purposes  be  neglected  especially  in  large-scale  operations 
where  many  drills  are  employed  and  the  output  is  conse- 
quently large.  In  estimating  power  costs  as  in  stoping  it 
is  customary  to  distribute  or  ' spread'  the  cost  and  charge 
an  equal  amount  to  each  machine  operating,  which  in  itself 
may  be  a  source  of  error  in  that  the  number  of  machines 
in  actual  operation  from  day  to  day  may,  together  with 
their  consumption  of  air,  vary  somewhat  causing  a  varia- 
tion in  computed  costs  to  be  charged  to  a  given  machine 
or  unit. 


COST  OF  STOPING  191 

The  cost  of  light  in  stoping  is  practically  a  constant 
quantity,  varying  but  slightly  in  the  various  districts,  and 
may  therefore  be  neglected  in  comparing  costs. 

The  value  of  cost  data  is  twofold,  namely,  it  may  be 
relative  and  comparative;  the  former  is  useful  as  showing 
the  relative  expenditures  for  various  kinds  of  work  in  the 
same  mine,  the  latter  may  serve  a  useful  purpose  in  the 
determination  of  the  cost  of  the  proposed  operations  in 
the  same  or  in  other  districts.  The  former  may  be  accurate, 
the  latter  may  be  very  inaccurate  and  unreliable  owing 
to  the  necessity  of  dealing  with  many  conditions  which  are 
largely  unknown  and  conjectural  at  best. 

The  question  as  to  how  cheaply  stoping  can  be  done,  or 
whether  it  can  be  done  as  cheaply  in  one  district  as  in  another 
or  in  different  mines  of  the  same  district,  will  have  to  be 
determined  by  ascertaining  the  cost  of  the  separate  items 
making  up  the  total  costs  in  the  cases  to  be  compared.  This 
may  be  accomplished  in  a  number  of  ways;  which  is  chosen, 
will  depend  largely  upon  the  accuracy  of  the  results  desired. 
In  order  that  cost  data  may  be  useful  they  must  indicate  an 
amount  or  expenditure  composed  of  a  number  of  regular 
factors  common  to  similar  operations  and  independent 
of  locality.  These  factors  to  be  of  the  most  value  should, 
for  comparative  purposes,  be  figured  on  a  percentage 
basis. 

There  are  two  methods  of  procedure  which  may  be  fol- 
lowed in  estimating  comparative  costs,  namely:  the  ton-day, 
-week,  or  -month;  and  the  percentage  methods;  the  latter 
being  based  on  total  yearly  or  semi-yearly  output. 


192  ORE  MINING  METHODS 

In  comparing  by  the  ton-day  -week  or  -month  method 
the  costs  of  two  similar  operations  in  different  districts  and 
computing  the  costs,  similar  items  of  cost  would  have  to  be 
known,  as  cost  of  labor,  supplies,  power,  etc.  In  one  case 
the  actual  tonnage  would  be  known,  while  in  the  case  being 
compared  the  tonnage  would  of  course  be  unknown.  The 
actual  difference  in  amount  of  work  done  would  then  be 
indicated  by  the  percentage  difference  in  labor  costs.  The 
estimated  difference  in  amount  of  work  done  gives  a  means 
of  calculating  the  cost  on  a  ton  basis. 

In  this  method  the  basis  for  calculation  is  labor  cost, 
which  is  held  by  some  to  be  the  real  basis  for  calculation 
of  costs.  There  are,  however,  serious  objections  to  this 
method  of  calculating  comparative  costs,  among  which  are 
the  following:  too  great  importance  given  to  labor  costs; 
other  items  of  cost  although  varying  considerably  do  not 
have  any  direct  influence  in  determining  costs  and  the  unit 
of  time  is  usually  too  short.  While  the  results  obtained  by 
the  application  of  the  method  are  not  exact,  yet  a  fair 
approximation  is  secured  which  usually  comes  close  to  the 
percentage  error  as  introduced  by  the  estimation  of  the 
character  of  work  that  can  be  done  in  various  formations 
and  which  amounts  in  the  majority  of  cases  to  mere  guess- 
work. 

In  a  somewhat  similar  manner  the  cost  may  be  dissected, 
being  divided  between  the  various  operations  as  stoping, 
haulage,  timbering,  hoisting,  etc.  The  expenditure  in  each 
case  is  subdivided  in  one  or  more  general  items,  as  labor, 
supplies,  power,  etc.,  and  is  distributed  proportionately 


COST  OF  STOPING  193 

among  the  several  items  of  operation  by  the  recording  of 
daily  costs.  The  principal  objection  to  the  method  arises 
from  the  difficulty  of  equably  distributing  or  spreading  the 
costs  over  the  various  operations.  A  common  method  of 
procedure  is  to  make  a  pro  rata  charge  to  each  operation 
proportionate  to  the  output  of  the  mine  or,  if  more  detail 
is  desired,  to  each  particular  level  and  even  to  the  various 
stopes  in  a  level.  Cost-keeping  is  a  strictly  engineering 
function,  and  when  an  attempt  is  made  as  in  the  last  men- 
tioned method  to  combine  it  with  bookkeeping  it  is  not 
strange  that  confusion  results. 

In  the  second  method  the  actual  costs  are  confined  to 
labor  costs  taken  from  the  pay-rolls  and  the  supply  accounts. 
In  stoping,  then,  there  would  be  a  certain  number  of  laborers 
at  given  wages,  the  sum  total  of  which  is  chargeable  to  the 
output.  In  a  similar  manner  under  supplies  the  various 
items  of  expenditure  are  listed  as  to  quantity  and  cost,  the 
total  expenditure  being  charged  to  output.  For  compara- 
tive purposes  the  total  cost  of  producing  a  certain  output 
is  taken  as  the  basis  for  calculation,  the  percentage  costs 
of  the  various  operations  indicating  the  amount  similar 
operations  exceed  one  another. 

COST  OF  STOPING  IN  VARIOUS  LOCALITIES 

Costs  of  stoping  in  a  number  of  the  large  mining  districts 
of  the  United  States  are  given  in  this  connection  and  bring 
out  some  interesting  facts  regarding  the  methods  of  cost- 
keeping  and  the  items  which  go  to  make  up  the  costs. 


194  ORE  MINING  METHODS 

The  Copper  Mines  of  Keweenaw  Point,  Michigan 

The  following  data  were  collected  by  the  author  during 
a  period  of  some  four  weeks  spent  in  the  Wolverine  Mine 
in  1906.  There  are  three  methods  of  stoping  employed  in 
this  mine  and  generally  throughout  the  district,  which  are: 
drift,  raise  and  cutting-out  stoping.  Drift  stoping  is  the 
usual  method  of  working  from  a  level  and  consists  in  carry- 
ing a  face  25  feet  wide  practically  the  full  height  of  the  lode; 
the  lower  part  includes  the  drift  and  is  run  at  the  required 
grade  of  the  level.  When  possible,  the  lower  or  drift  portion 
is  attacked  first,  thus  forming  a  sump  or  opening  into  which 
the  remaining  upper  portion  may  be  broken.  The  average 
of  the  total  length  of  holes  drilled,  in  the  cases  observed, 
was  1 74  feet,  while  the  time  of  drilling  averaged  from  obser- 
vations on  9  holes  in  each  case  was  as  follows: 

Average  depth  of  hole 5.6  feet 

Mins.     Sees. 

Total  time  of  drilling,  per  hole 41         47 

Delays  in  drilling,  per  hole 19         29 

Actual  time  drilling  i  foot  of  hole 7         27 

The  total  time  of  drilling  174  feet  of  hole  was,  therefore, 
21  hours  and  45  minutes,  or  two  shifts. 

Stoping  is  paid  for  by  the  fathom,  the  exact  amount 
varying  with  the  particular  stope;  the  price  runs  from  $5.50 
to  $9  and  averages  probably  $8  per  fathom.  A  fathom  is 
6X6X6  feet  or  216  cubic  feet,  8  cubic  yards.  The 
average  height  of  stope  is  12  feet,  and  the  miners  are  paid 
for  this  height  regardless  of  whether  the  actual  height  is 
higher  or  lower.  The  width  of  the  drift  is  subtracted  from 
the  width  of  the  stope  and  is  paid  for  as  drifting,  $5.50  being 


COST  OF  STOPING 


195 


the  usual  rate  per  foot.  The  miner  then  receives  $8  per 
fathom  for  19  feet  width  of  stope  12  feet  high,  and  $5.50 
per  foot  for  drift  6  feet  wide  and  1 2  feet  high. 

The  174  feet  of  holes  when  charged  and  fired  usually 
break  4^  fathoms  or  36  cubic  yards  of  ore,  the  result  of  two 
shifts'  work.  The  delays  due  to  cleaning  up  and  other  causes 
may  reduce  the  output  somewhat,  but  it  is  seldom  less 
than  one-half  or  to  about  2\  fathoms  per  shift.  Working 
two  shifts  per  day,  as  is  the  practice,  58 \  fathoms  are 
broken  down  per  month  of  26  working  days.  At  $8  per 
fathom  this  gives  $468  per  month  for  two  crews  of  two  men 
each,  and  from  it  all  expenses  have  to  be  deducted.  The 
two  crews  employ  a  drill  boy  between  them.  The  $4  charge 
for  drill  steel  is  also  divided  between  the  two  crews,  both 
crews  using  the  same  drill.  The  following  are  the  itemized 
expenses  of  one  crew  during  one  month  when  40  fathoms  or 
320  cubic  yards  of  ore  were  taken  out: 


Total. 

Per 
Fathom. 

Per 
cu.  yd. 

7  boxes  powder  at  $i  7  oo 

Sno  oo 

$2    Q7C 

$O    372 

2  boxes  candles  at  $8  oo 

1  6  oo 

o  40 

O   O^ 

800  feet  fuse  at  i  cent            

8.00 

O    2O 

O.O2S 

200  caps    

4.00 

O.  IO 

O.OI25 

T.  gallons  oil  at  30  cents 

o  oo 

O    O2^ 

O    OO^ 

Steel 

2    OO 

O    O< 

o  0062 

Drill  boy                                             

I  "?    OO 

o    37? 

o  04.7 

Total      

$164.  QO 

$4.  122 

$o.  si? 

It  will  be  seen  that  350  pounds  of  powder  were  used  to 
remove  320  cubic  yards  of  ore,  or  1.09  pounds  per  cubic 
yard.  Referring  to  the  above  cost  of  $4.122  per  fathom, 


196 


ORE  MINING  METHODS 


it  may  be  noted  that  the  average  of  a  number  of  accounts 
gave  an  average  of  $4.24  per  fathom. 

In  raise  stoping  the  work  is  more  difficult  and  consequently 
the  cost  is  higher,  while  in  cutting-out  stoping  the  reverse  is 
true  and  the  cost  is  correspondingly  less.  The  price  paid 
per  fathom  is  the  same  as  with  other  stoping  operations. 
When,  however,  the  ground  breaks  readily  and  the  stopes 
are  large,  the  amount  paid  may  be  reduced,  even  as  low 
as  $5.50  per  fathom,  while  under  less  favorable  conditions 
a  higher  price  may  be  paid. 

The  usual  practice  in  the  district  is  to  pay  the  miner  on 
beginning  work  $60.00  per  month  for  the  first  two  months' 
work,  at  the  end  of  which  time  his  work  is  measured  up  and 
he  is  paid  $8  (or  the  amount  agreed  upon)  per  fathom  for 
stoping  and  $5.50  for  drifting  (in  drifting  and  drift  stoping). 
In  all  contracts  the  miners  furnish  supplies,  the  company 
providing  drills  and  steel. 

The  cost  of  stoping  in  a  number  of  mines  in  the  same 
district  and  for  the  years  1887  and  1892  are  shown  in  the 
following  tabulation: 


Mine. 

Year. 

Contract 
Price  per 
Fathom. 

Osceola            

1887 

$o.Ql 

Osceola      

1892 

11.09 

Atlantic 

1802 

3.Q8 

Kearsarge 

1802 

0-  ^7 

Tamarack                

1802 

11.86 

Average  

$9.28 

The  ore  is  hard  and  does  not  drill  or  blast  very  easily. 


COST  OF  STOPING  197 

The  Cripple  Creek  District,  Colorado 

The  distribution  of  costs  of  stoping  per  ton  in  the  Port- 
land gold  mine  as  given  for  the  year  1906  is  as  follows: 

Cost  per  Ton. 

Labor $i . 142 

Machines o .  270 

Tramming o .  029 

Explosives o .  380 

Hoisting o .  230 

Supplies o .  036 

Superintendency,  assaying,  surveying,  etc o .  450 


Total $2.537 

The  labor  costs  may. be  analyzed  as  follows: 

Machine  men $0.4761 

Trammers 0.3214 

Pipe  and  track  men °-°357 

Timbermen o.  1666 

Timber  helpers o.  1428 


Total $i .  1426 

The  ore  is  moderately  hard,  but  drills  and  blasts  readily. 

It  is  evident  on  examining  the  above  account  that  the 
work  is  thoroughly  systematized,  the  idea  being  to  dis- 
tribute to  each  and  every  operation  involved  its  propor- 
tionate amount  of  expense.  There  is  also  indication  of  a 
' spread7  of  costs,  especially  in  the  items  of  machine  drills, 
tramming,  hoisting,  superintendency,  etc.  It  is  obvious 
that  with  such  a  system  a  very  effective  check  upon  the 
various  operations  is  possible. 


198  ORE  MINING  METHODS 

The  Alaska-Treadwell  Mines,  Douglas 
Island,  Alaska 

The  successful  operation  of  the  large  gold  mines  of 
Douglas  Island,  Alaska,  is  made  possible  by  a  number  of 
conditions,  among  which  none  is  of  more  importance  than 
that  of  organization. 

The  large  scale  of  the  operations  and  the  comparative 
low  grade  of  the  ore  pract  cally  necessitate  very  careful  and 
systematic  management  in  order  that  the  work  may  be 
profitably  carried  on.  The  figures  given  below  are  for  the 
years  1901  and  1902. 

Cost  per  Ton. 

Machine  work $o .  3793 

Rock  breaking 0.3124 

Tramming o .  0359 

Hoisting o .  0486 

Explosives o.  2269 

Light o .  0085 


Total $1.0116 

Ore  is  hard  and  firm,  but  drills  and  blasts  quite  easily. 

Here,  as  in  the  last  mentioned  case,  an  attempt  has  been 
made  to  distribute  costs,  charging  to  each  operation  the 
proportionate  amount  of  expenditure,  but  unless  the  dis- 
tribution of  costs  is  carefully  made  considerable  confusion 
and  inaccuracy  may  result. 


COST  OF  STOPING 


199 


The  Lead-Silver  District,  Cceur  d'Alene,  Idaho 

The  detailed  cost  of  stoping  in  the  Bunker  Hill  and  Sulli- 
van Mine  for  the  year  1908  is  as  follows: 


Details  for  Labor  and 
Supplies. 

Total  for 
the  Year. 

Average 
per  Ton  for 
the  Year. 

Highest  Cost 
per  Ton  for 
I  Month 
During  the 
Year. 

Lowest   Cost 
per  Ton  for 
i  Month 
During  the 
Year. 

Foremen,  bosses,  black- 
smiths,       machinists, 
tool-packers,  etc  
Timberman     and     car- 
penters 

$60,982.27 

25,109.38 
125,148.48 
15,918.00 

jss^yo-s0 
7,708.40 
7,492.70 

3o>oi9-37 
7,482.08 
1,329.87 
4,158.20 
11,667.61 
61,629.00 
7,876.30 
9,292.80 
2,297.20 

$0.185 

0.076 

o-379 
0.048 
0.403 
0.023 
0.023 
0.091 
0.023 
0.004 
0.013 
0.035 
0.186 
0.024 
0.028 
0.007 

$0.191 

0.082 
0.400 
0  .  042 
0.450 
0.027 
0.025 
O.III 

0.026 
0.004 
0.014 
0.032 

0.199 

0.024 

0.030 

0.007 

$0.165 

0.063 

o-339 
0.058 

0-379 

0.021 
0.021 
0.087 
0.017 
0.006 
O.OI2 
0.025 

o.  165 
0.027 

0.030 

0.006 

Miners  

Car-men  

Shovelers  
Power  labor  

Repair  labor 

Explosives 

Illuminants 

Lubricants. 

Iron  and  steel  

Miscellaneous  supplies.  . 
Timber  and  lagging.  .  .  . 
Power  supplies  
Wood 

Stable  and  stock 

Total  

$511,288.16 

$1.548 

$1  .  664 

Nov. 

$1.421 

May. 

Ore  is  not  particularly  hard  to  drill  and  blast. 

The  comparatively  high  cost  of  timber  as  shown  in  the 
above  table  is  due  to  the  fact  that  square-set  timbering  is 
an  important  adjunct  to  the  mining  of  the  ore  in  this  district. 
The  high  cost  of  labor,  particularly  for  shovelers,  is  due  to 
the  necessity  of  freeing  the  stopes  from  ore  and  placing 
waste-filling. 


200  ORE  MINING  METHODS 

The  Goldfield  Consolidated  Mines  Company, 
Goldfield,  Nevada 

The  costs  of  stoping  during  ten  months  of  1909  are  given 
in  the  following  tabulation: 

Cost  per  Ton. 

Labor $i .  24 

Supplies o .  66 

Power o .  03 

Department o.  25 

Construction o .  02 

General . .  o.  18 


Total $2.38 

Ore  is  a  fair  average  for  drilling  and  blasting. 

The  first  three  items  given  are  regular  and  legitimate 
cost  for  this  kind  of  work;  the  last  three  are  indeterminate, 
and  while  they  may  be  composed  wholly  or  in  part  of  ex- 
penditures necessary  for  the  proper  carrying  on  of  the  work 
of  stoping,  yet  their  designation  leaves  this  in  doubt. 

The  Joplin  Lead-Zinc  District,  Missouri 
The  cost  of  breaking  ground  in  the  Joplin  district  varies 
considerably  owing  to  character  of  ground,  which  ranges 
from  very  hard  to  very  soft.     The  usual  conditions  existing 
in  the  sheet  ground  in  the  vicinity  of  Joplin,  Webb  City, 
etc.,  permit  the  ore  to  be  broken  down  at  moderate  cost. 
The  following  costs  are  representative  of  the  district: 


COST  OF  STOPING  2OI 

COST    OF    STOPING    IN    1901 

2  machine  men  at  $3.00 $6 .  oo 

2  machine  helpers  at  $2.50 5 .  oo 

2  shovelers  at  $2.50 5 .  oo 

i  blacksmith  at  $2.50 2 . 50 

i  ground  boss  at  $3.00 3 .  oo 

Explosives 6 .  oo 

Incidentals 3 .  oo 


Total $30 . 50 

Drilling  and  blasting  fairly  easy,  although  variable,  owing 
to  character  of  ground  encountered. 

The  $30.50  represents  the  expenditure  for  one  day  when 
75  tons  of  ore  are  broken;  the  cost  per  ton  was  then  about 
$0.40. 

Other  more  detailed  costs  of  operations  that  go  to  make 
up  the  cost  of  breaking  ground,  also  related  cost  data  ex- 
pressed in  cents  per  ton,  are  as  follows: 

COST    OF    STOPING    IN    1903 

Cost  of  drilling,  hand  work $0.06800 

Cost  of  drilling,  machine  work 0.05600 

Cost  of  drill  steel o .  00878 

Cost  of  powder,  caps  and  fuse o .  04050 

Cost  of  oil  for  lamps o .  00080 

Cost  of  timbering,  soft  ground o. 00045 

Cost  of  pumping,  mine  pumps o .  00005 

Cost  of  track o .  00009 

Cost  of  shoveling o .  03900 

Cost  of  labor  underground o.  19890 

Cost  of  hoisting o .  02860 

Cost  of  tramming 0.02600 

Cost  of  air  compressor 0.00150 

Total $0.46867 

The  cause  of  the  variation  of  7  cents  per  ton  noted  above 
is  difficult  to  explain,  but  is  slight  when  the  factors  influ- 
encing the  costs  are  considered.  The  period  during  which 


202  ORE  MINING  METHODS 

the  figures  from  which  the  averages  were  calculated  is  a 
controlling  factor  if  short,  otherwise  not. 

The  War  Eagle  Mine,  British  Columbia 

The  costs  previously  given  are  for  mines  located  in  the 
United  States.  The  cost  of  stoping  as  given  in  the  company's 
report  of  the  War  Eagle  Mine  for  the  year  1909  illustrates, 
even  to  better  advantage  than  in  the  previous  cases  cited, 
the  spread  of  costs,  involving  practically  all  operations 
having  to  do  with  the  underground  work.  The  following 
costs  are  figured  on  a  ton  basis: 

1.  Drilling $i-53 

2.  Tramming  and  shovelling o.  53 

3.  Timbering o .  29 

4.  Hoisting o .  13 

5.  Smithing o.  15 

6.  Ore  sorting o.oi 

7.  General  labor o .  30 

8.  Air 0.21 

9.  Candles  and  illuminating  oil 0.03 

10.  Explosives 0.02 

11.  Drills  and  fittings.  .  . 0.25 

12.  Mine  supplies 0.05 

13.  Lumber  expense o .  04 

14.  Stable  and  teaming o .  03 

15.  Assaying o .  04 

1 6.  Surveying o .  05 

17.  Electric  lighting 0.02 

18.  Salaries o .  03 

19.  Office  expenses o.  18 

20.  General  expenses 0.05 

Total $3.95 

Ore  drills  and  blasts  moderately  well. 
In  comparing  this  cost  of  stoping  with  others  which  have 
not  been  so  extensively  distributed  it  would  be  necessary 


COST  OF  STOPING  203 

to  eliminate  a  number  of  items,  those  chosen  for  actual  use 
being  i,  5,  8,  9,  10,  n  and  12.  The  items  2,  3,  and  6  might 
very  properly  in  this  case  be  included,  especially  3,  as  square- 
set  timbering  is  employed.  The  item  of  drilling  is  probably 
labor  of  operating  drills,  while  the  air  item  indicates  the 
cost  of  power.  Drills,  fitting  and  mine  supplies  consist 
of  steel  and  other  drill  repairs. 

An  examination  of  the  above  data  brings  out  the  fact 
that  the  larger  the  company,  and  consequently  the  operation, 
the  more  detailed  are  the  working  costs,  which  is  not  shown 
to  particularly  good  advantage  either  owing  to  the  com- 
bining of  certain  costs  in  this  connection.  By  increasing 
the  number  of  items  in  an  operation  and  putting  the  collec- 
tion of  the  data  upon  which  the  costs  are  based  in  the  hands 
of  a  sufficient  number  of  competent  men  it  is  possible  to 
secure  fairly  accurate  results,  but  there  is  always  danger  of 
lax  work  being  done,  short  cuts  being  taken  and  approxi- 
mations made,  which  if  persisted  in  mean  inaccurate  and 
untrustworthy  returns.  Another  cause  of  error,  aside  from 
poor  organization  of  the  data-collecting  force  and  arising 
from  the  distribution  of  costs,  is  that  often  no  account  is 
taken  of  variations  in  work  done  by  the  factors  involved. 
This  can  be  illustrated  by  the  one  item  of  power,  the  cost 
of  which  is  commonly  distributed  uniformly  over  all  the 
machines  of  a  kind,  as  machine  drills  in  stoping.  It  is  rarely 
the  case  that  out  of  100  or  even  50  drills  employed  in  stop- 
ing,  all  are  being  operated  at  the  same  time,  i.e.,  continu- 
ously day  after  day.  An  ordinary  piston  drill  is  seldom 
running  more  than  one-half  the  time  that  it  is  supposed  to 


204  ORE  MINING  METHODS 

be  in  operation.  The  advent  of  the  air-hammer  drill,  which 
is  now  being  largely  employed  in  stoping  operations,  might 
be  supposed  to  change  these  conditions,  for- where  used  in 
similar  work  as  the  piston  drill  it  is  running  the  greater 
part  of  the  time.  It  would  seem  that  the  consumption  of 
air  would  be  greater,  and  so  it  would  were  it  not  for  the 
fact  that  the  consumption  of  air  is  less,  approximately  one- 
half  that  of  a  piston  drill.  Where  continuous  operation 
is  maintained  under  conditions  such  as  permit  the  drilling 
of  a  greater  footage  than  with  piston  drills,  there  would  have 
to  be  a  different  unit  of  cost  calculated  if  the  two  types  of 
drills  were  operating  in  the  same  mine,  which  would  lead 
to  still  further  complication  in  the  estimation  of  costs  of 
power.  Further,  the  power  required  for  each  drill  varies 
considerably  both  with  its  period  of  service  and  the  skill 
and  experience  of  its  operators,  and  to  a  less  extent  with 
its  distance  from  the  source  of  power,  as  in  the  use  of  air 
drills.  In  order,  then,  to  show  the  correct  cost  of  power  for  a 
drill  employed  in  stoping  it  is  necessary  to  know  at  least  the 
number  of  drills  that  are  in  actual  operation,  which  can 
only  be  determined  by  daily  inspection.  This  requires  a 
constant  and  often  daily  change  of  unit  costs,  which  is 
somewhat  confusing.  A  fair  and  uniform  charge  per 
drill-shift  is  probably  preferable,  which  unit  cost  multiplied 
by  the  number  of  units  will  at  once  give  the  power  cost 
desired. 

The  cost  per  drill-shift  for  various  styles  of  compres- 
sors and  at  different  altitudes  is  given  in  the  following 
table. 


COST  OF  STOPING 


205 


Cost  per  loco  cu. 
ft.  Free  Air,  Com- 

Cost per  Drill- 

oViiff 

pressed. 

snitt. 

Maximum 

Total 

Style  of 
Compressor. 

Capacity, 
cu.  ft.  Free 
Air  per 

Cost 
per 
H.P. 

Sea 
Level. 

5000 
ft. 

alt. 

10,000 
ft 
alt. 

Sea 
Level. 

5000 
ft. 
alt. 

10,000 

ft. 
alt 

Minute. 

Hour. 

cents. 

cents. 

cents. 

cents. 

dols. 

dols. 

dols. 

Simple  steam 

(non-condensing) 

200 

2.2 

5-9 

5-3 

4.8 

2.07 

2.  22 

2.40 

Compound  steam 

•    (non-condensing) 

300 

i-5 

4.0 

3-6 

3-3 

1.40 

1.50 

1.65 

Simple  steam 

(condensing).  .  .  . 

2500 

I.O 

2.7 

2.4 

2.2 

-95 

I  .01 

I.  10 

Compound  steam 

(condensing)  .... 

3000 

0.8 

2.  2 

1.9 

1.8 

.76 

.81 

.88 

Three-inch  drill  taken  as  standard.  Eight-hour  shift  time  of  working.  Cost 
of  coal,  $5.00  per  ton. 

The  cost  will  vary,  of  course,  with  the  character  of  rock 
or  ore  drilled.  The  above  figures  were  calculated  from  data 
collected  from  work  done  in  granite.  The  compressors  are 
all  two-stage,  intercooled. 

The  differentiation  between  cost  of  various  operations, 
rendering  each  account  simple  and  complete  in  itself,  would 
seem  desirable.  Tramming,  hoisting,  etc.,  might  readily 
be  placed  under  a  class  of  operations  separate  from  stoping, 
as  handling  ore  outside  the  stope.  In  other  words,  charge 
to  stoping  just  those  operations  that  are  confined  to  the 
stopes,  thus  localizing  the  operations  and  their  costs.  Sim- 
plicity, both  with  regard  to  the  management  of  the  work 
and  the  collection  of  data  upon  which  costs  are  figured,  is 
of  probably  the  most  importance,  and  this  can  be  effected 
to  good  advantage  by  contract  work,  where  the  miner  keeps 
his  own  accounts  largely,  or  at  least  is  sufficiently  inter- 
ested to  keep  close  check  upon  them.  The  operator,  in 


206 


ORE  MINING  METHODS 


turn,  checks  off  results  as  the  output  resulting  from  the 
miners'  labor,  and  pays  for  work  actually  done.  The  con- 
tract work  previously  mentioned  as  in  the  case  of  the 
Wolverine  Mine  illustrates  the  point. 

The  two  general  contract  systems  employed  are:  measure- 
ment of  volume,  as  '  advance '  in  drifting  and  volume  of  ore 
broken  in  stoping;  and  the  hole-contract,  i.e.,  the  measure- 
ment of  the  number  of  feet  of  hole  drilled.  The  following 
data  show  the  saving  effected  by  the  employment  of  the 
contract  system  in  place  of  the  wage  system  in  stoping  as 
was  done  in  the  Center  Star  and  War  Eagle  mines  of  Ross- 
land,  British  Columbia: 


Contract 
(hole)  System, 
per  Ton. 

Wage  System, 
per  Ton. 

$0   -1*6 

f     d 

Blasting 

O    O2I 

$0.750 

Explosives            .                                               

O.  IOO 

o.  nc; 

Total                                         

$o.  477 

$0.865 

The  advantage  gained  by  the  company  was  also  a  gain 
for  the  miner  in  that  his  daily  wage  was  increased  from 
$4  to  $4.25,  as  against  $3.50  under  the  wage  system.  The 
increased  wage  shows  both  a  saving  per  ton  in  cost  of  stop- 
ing and  an  increased  tonnage  of  ore  broken,  a  natural  result 
due  to  better  pay,  as  previously  indicated. 

It  might  be  stated  in  this  connection  that  the  contract 
system,  in  which  the  miner  is  paid  by  the  fathom  or  other 
unit  of  volume,  has  proven  unsatisfactory  in  these  mines 
owing  to  the  difficulty  of  measuring  exactly  the  volume  of 


COST  OF  STOPING 


207 


ore  broken  in  the  very  irregular  stopes  —  the  pay-shoots 
being  very  irregular  in  outline. 

COST  OF  SUPPORT  IN  STOPES 

In  certain  kinds  of  work,  as  working  slightly  dipping 
deposits,  square-set  mining,  etc.,  the  cost  of  support  may  be 
a  necessary  and  important  part  of  the  cost  of  breaking  ore 
or  stoping,  being  usually  figured  on  the  tonnage  basis.  A 
single  case  will  suffice  to  show  the  cost  per  ton  under  average 
conditions,  and  for  comparative  purposes  the  cost  under 
two  different  systems  of  working  are  given.  The  figures 
given  below,  prepared  by  Mr.  B.  C.  Yates,  are  for  the  old 
square-set  method  and  a  more  recent  method  now  being 
largely  employed  in  the  Homestake  mines  of  South  Dakota. 

AMOUNT    AND    COST    OF    TIMBER,    SQUARE-SET    METHOD 


Name  of  Piece. 

Number 
of 
Pieces. 

Lineal  Feet 
or  Feet 
Board 

Measure. 

Cost  of 
Material. 

Labor, 
Sawing 
and 
Framing. 

Total. 

Sill-floor  posts  

421 

3,650 

$474.  50 

$06.83 

$^7l  .  33 

Upper  floor  posts.  .  . 
Caps     . 

2,077 
2,410 

16,616 

13,  2CC 

2,160.08 
1,723.  1C 

477-71 
506  10 

2»637  -79 

2  22O    2  ? 

Ties  

2,261 

12,43s 

1,616.  ex 

474.81 

2  OQI     36 

Sills,  203  long,  382 
short 

A  537 

226  85 

22    60 

Lastjinsr 

13,020 

75  006 

37QC    -30 

770     c  -} 

41  74.    83 

Lagging  strips  
Wedges  
47  sill-floor  chutes, 
complete 

2,410 
2.352 

4,025 
784 

64.82 
13-33 

3ii  68 

30.00 
11.76 

16  25 

94.82 
25.09 

215  upper-  floor  bins, 
complete 

786    22 

37    QO 

6*  1  -yo 
824   12 

Ladders 

14 

H7 

I  .QO 

3    to 

54O 

Labor  placing  tim- 
bers and  chutes  .  . 

4  74^    OO 

Breakage  (10%)  of 
lagging,  5%  posts, 
caps  and  ties 

7Q7      Q7 

Totals 

$11  174.   47 

$2  O57    08 

$-18  770  (J2 

208 


ORE  MINING  METHODS 


AMOUNT    AND    COST    OF   TIMBER,    HOMESTAKE    METHOD 


Name  of  Piece. 

Number 
of 
Pieces. 

Lineal 
Feet  or 
Feet  Board 

Measure. 

Cost  of 
Material. 

Labor, 
Sawing 
and 
Framing. 

Total. 

Sill-floor  posts  

421 

3,6co 

$474.50 

$96.83 

$C7I.33 

Caps 

4.IO 

2,2C.O 

2Q3.  JC 

86  10 

•270    2C 

Ties        

^Si 

2,00? 

272.  3C, 

80  01 

3C2     36 

Sills,  long      

2O3 

^,«-.y^ 
2,436 

121.  80 

12.  18 

133    08 

Sills,  short  

382 

2,IOI 

IOC  .OC 

IO.  <O 

IIC.CC 

Lagging.  . 

1,71:2 

IO,2I4 

c.io.  70 

^1  .07 

^61  .  77 

Lagging  to    protect 
track 

764. 

A  4C4 

222    70 

22    27 

24.4.  07 

Relief  lagging 

1,684 

13,472 

673    60 

67     36 

740  06 

Wedges  

200 

66 

I.  12 

I  .00 

2.  12 

Totals  

$2,674.97 

$427.32 

$3,102.29 

AMOUNT   AND    COST    OF    TIMBER    IN    MAN-WAYS,    HOME- 
STAKE    METHOD 


Name  of  Piece. 

Number 
of 
Pieces. 

Lineal 
Feet  or 
Feet  Board 
Measure. 

Cost  of 
Material. 

Labor, 
Sawing 
and 
Framing. 

Total. 

Upper-floor  posts.  .  . 
Caps 

96 

48 

768 
264 

$99.84 
34    32 

$22.08 
10  08 

$121.92 
44   40 

Ties      

48 

264 

34    32 

10  08 

44  40 

Lagging,  floors  
Lagging,  sides  
Drift  pins  

96 

720 
1,440 

560 

4,197 
4C7  Ibs. 

28.00 
209.85 
22.  8C 

2.80 
20.98 

30.80 
230.83 

22.81; 

Ladders 

28 

2  3C 

4OO 

7    OO 

1  1    OO 

Labor  standing  sill- 
floor  timbers  .... 

?q8  16 

Totals 

$3  108  i< 

$C.OO    34. 

$4.  ^66    6^ 

The  costs  of  the  two  methods  were  $0.257  and  $0.060 
per  ton  figured  on  an  output  of  73,000  tons  from  the  stope, 
thus  showing  a  saving  of  $0.197  per  ton  in  favor  of  the 
Homestake  method. 

Comparative  costs  of  a  stope  in  a  Cripple  Creek  gold 
mine  where  stulls  and  filling  were  used  are  given  in  the 
following  table. 


COST  OF  STOPING  209 

STULLED  STOPE 

143  stulls  at  $2.50 $357-5° 

Lagging 10.00 

Total $367-5° 

FILLED    STOPE 

Interest  on  $4640  for  4.5  months  at  6  per  cent $104.40 

Timber  (one-third  of  $357 . 50) 1 19 . 1 7 

Total $223 . 57 

Saving  in  favor  of  the  filled  stope  $143.93.  The  filled 
stope  had  in  this  case  a  filling  of  ore  valued  at  $20  per  ton, 
which  is  considered  as  so  much  capital  tied  up  for  the  time 
being.  As  G.  E.  Wolcott,  who  furnishes  these  data,  points 
out,  there  is  comparatively  small  difference  between  the 
two  cases  when  considered  from  the  standpoint  of  amount 
of  ore  broken.  Further,  there  is  a  greater  difference  with 
low-grade  and  a  less  with  higher  ore,  which  with  the  high- 
grade  ore  may  even  reach  a  point  where  the  method  of 
support  by  stulls  may  be  cheaper  than  with  filling.  Aside 
from  the  consideration  of  costs  there  is  a  decided  advantage 
in  favor  of  ore-filled  stopes  or  the  so-called  '  reserves '  of 
ore,  where  the  conditions  are  suitable  for  such  a  method  of 
working.  Aside  from  facilitating  work  at  the  face,  in  con- 
venience of  placing  and  setting  up  drills  and  giving  the 
miner  ready  access  to  the  working  face,  its  great  advantage 
lies  in  the  regulation  of  output  of  the  mine. 


INDEX 


Air  hammer  drill  in  stoping,  204. 
Alaska-Treadwell  mines,  100,  104. 

depth  of  open-cuts,  156. 

milling  method  in,  179. 
Angle  of  repose,  77,  78. 
Angle  of  underlie,  9. 
Arch  pillars,  7,  32,  40. 

in  Combination  Mine,  66. 

in  Homestake  Mine,  124,  125,  126. 

in  Trimountain  Mine,  88. 
Arching  of  roof,  19. 

dome  of  equilibrium,  19. 

in  Homestake  Mines,  124,  129. 

in  iron  mines,  milling  method,  178. 
Atlantic  Mine,  85. 

Back  of  stopes,  43. 

in  Alaska-Treadwell  mines,  103. 
Back-filling  method,  advantage  and  dis- 
advantage of,  in  St.  Lawrence  Mine, 
84. 
Back-stoping,  in  Combination  Mine,  64. 

in  Hecla  Mine,  68. 
Baltic  Mine,  85. 
Battery  of  stulls,  10. 
Bedded  deposits,  stoping  in,  32. 
Benches  in  stopes,  42. 

height  of,  34. 

Bessemer  and  non-Bessemer  ore,  141. 
Bingham  Canyon  mines,  141,  179. 

steam  shovel  work  in,  166. 
Bii-mingham  iron  mines,  Ala.,  56. 
Blasts,  mammoth,  160,  161. 
Blind  drifts  in  Alaska-Treadwell  mines, 

IQI. 

Blocking  in  Hecla  Mine,  68. 
Breaking  ore,  38,  55. 

bull-dozing,  175. 

cost  of,  183. 

in  Glory-hole  mining,  177. 

in  iron  mines,  Ala.,  58,  59. 

in  Lake  Superior  iron  mines,  136. 

in  milling  method,  1 74. 

in  open-cut  work,  hand  mining,  160, 
161,  169. 

method  of  contracting  for,  189. 
Breaking-through  in  stoping,  57,  87. 


Breast  stoping: 

advantage  of,  42. 

appli cation,  42. 

disadvantage  of,  42. 
Broken  Hill  mines,  Australia,  no,  119. 
Bulkheads: 

advantages  of,  21. 

disadvantages  of,  21. 

used  with  filling,  12. 
Bull-dozing  in  Alaska-Treadwell  mines, 
103. 

in  Glory-hole  mining,  175. 
Bunker  Hill-Sullivan  mines,  72. 
Butte,  Montana,  187. 

Cantilever  support  for  back  of  stope,  115. 
Caving: 

advantages  of,  22. 

Bingham  Canyon  mines,  141, 145, 146. 

disadvantages  of,  22. 

in  diamond  mines,  148,  152. 

in  Lake  Superior  iron  mines,  132,  133. 

in  Mercur  mines,  Utah,  90,  92. 

in  Susquehanna  Mine,  139. 

methods,  5,  19. 

when  applicable,  5. 
Central  Mine,  Mo.,  186. 
Chambers  in  diamond  mines  of  South 

Africa,  153. 

Chinaman  ore  chute,  53. 
Chutes: 

block-holes,  50. 

branched,  51,  73,  75, 143, 146. 

broken-slope,  51. 

Chinaman,  53. 

cribbed,  78. 

distance  apart,  66,  75. 

for  loading  cars,  53. 

in  Bingham  Canyon  mines,  143. 

in  Broken  Hill  mines,  113, 115. 

in  Bunker  Hill-Sullivan  mines,  75. 

in  Cceur  d'Alene  mines,  73. 

in  Gold  Prince  Mine,  98. 

in  Homestake  mines,  125. 

in  Lake  Superior  mines,  132. 

in  milling  method,  173. 

in  St.  Lawrence  Mine,  81,  83. 


211 


212 


INDEX 


Chutes: 

in  Tonopah  Mine,  62. 

mill  holes,  175, 180. 
in  Trimountain  Mine,  87. 

sheet  metal,  46. 

stoppage  of,  64. 

timber,  70. 

Coeur  d'Alene  mines,  Idaho,  67. 
Combination  Mine,  Goldfield,  Nev.,  64. 

milling  method,  179. 
Combined  stoping: 

advantages  of,  43. 

disadvantages  of,  43. 

limits  of,  43. 
Comstock  Lode: 

square-sets  and  filling,  4. 

temperatures  of ,  186. 

timbering  in  mines,  3. 
Contract  systems,  189,  206. 
Conveyors  in  stopes,  46. 

the  monorail,  46. 

Corrals  of  waste  in  Hecla  Mine,  70. 
Cornish  system  of  stoping,  30,  31. 
Corduroy  in  Comstock  Lode,  3. 
Costs: 

contract  stoping,  189. 

detailed,  187,  188. 

drill-shift,  204. 

factors  influencing,  183,  184,  188. 

in  Alaska-Treadwell  mines,  198. 

in  Cceur  d'Alene  mines,  190. 

in  Copper  mines  of   Michigan,  194, 
196. 

in  Cripple  Creek  mines,  197,  208,  209. 

in  Goldfield  Mine,  Nevada,  200. 

in  Joplin  district,  Missouri,  200. 

in  War  Eagle  Mine,  B.  C.,  202,  206. 

method  computing,  191,  203,  205. 

of  breaking  ore,  183,  185. 

of  labor,  effect  on  stoping,  186,  197, 
199. 

of  power,  190,  203. 

of  stoping,  184,  189,  193,  194,  198, 

199,  200,  201,  202,  207. 
in  various  localities,  193. 

of  supplies,  190. 

of  support,  184,  207. 

of  timber,  199. 

value  of  data,  191. 
Covers  in  open-cut  mining,  164. 

thickness  of,  164. 
Cribs: 

advantages  of,  21. 

crib- work  in  Broken  Hill  mines,  114, 

.115,  117- 

disadvantages  of,  21. 
in  stopes,  12. 
used  with  filling,  12. 


Cripple  Creek: 

cost  of  stoping,  208,  209. 
Cross-cuts,  77,  78. 

in  Alaska-Treadwell  mines,  101. 

in  Broken  Hill  mines,  113,  117. 

in  Gold  Prince  Mine,  97. 

in  Homestake  mines,  121. 

in  Lake  Superior  mines,  132,  133, 138. 

in  mines,  77,  78. 

in  St.  Lawrence  mines,  81. 
Cutting-out  stoping: 

at  Keweenaw  Point,  194. 

in  Alaska-Treadwell  mines,  103 

in  Combination  Mine,  64. 

in  Trimountain  Mine,  87. 

Dams: 

for  holding  back  waste,  125. 

for  holding  back  bad  ground,  139. 
Dead-ends,  8. 

Depth  of  mining,  open-cut,  156. 
Development: 

in  Alaska-Treadwell  mines,  100. 

in  Baltic  and  Trimountain  mines,  85. 

in  Bingham  Canyon  mines,  143. 

in  Broken  Hill  mines,  113,  115,  117. 

in  Coeur  d'Alene  mines,  73,  75. 

in  diamond  mines  of  S.  Africa,  149, 
152. 

in  Gold  Prince  Mine,  Colo.,  97. 

in  Homestake  mines,  121. 

in  Lake  Superior  iron  mines,  top-slice 
method,  132. 

in  Lake   Superior  iron   mines,   sub- 
drift  method,  135. 

in  Mercur  mines,  90,  91. 

in  milling  method,  173. 

in  Queen  Mine,  107. 

in  steam-shovel  mining,  168. 

in  St.  Lawrence  Mine,  Butte,  Mont., 
81. 

in  Susquehanna  Mine,  Minn.,  139. 

in  Zaruma  Mine,  Ecuador,  77. 
Diamond,  bearing  formations,  148,  149, 

152,  154. 
Diamond  mines  of  S.  Africa,  148. 

pipes  and  ducts,  148,  149. 
Disposal  of  waste : 

in  open-cut  work,  165. 
Docks: 

in  open-cut,  hand  work,  158. 

in  open-stopes,  45. 
Dome  of  equilibrium,  19. 

arching  of  roof,  19,  184. 

in  underground  milling  method,  178. 

when  used,  19. 
Drainage: 

in  strip-pits,  165. 


INDEX 


213 


Drifts: 

blind,  101. 

distance  apart,  135. 

in  diamond  mines,  152,  153. 

in  Alaska-Tread  well  mines,  101. 

in  Bingham  Canyon  mines,  146. 

in  caving  pillars,  145. 

in  diamond  mines  of  S.  Africa,  152. 

in  Lake  Superior  iron  mines,  133. 

in  stopes,  101,  103. 
Drill-shift  in  stoping,  204,  205. 
Dry- walls  in  copper  mines,  85. 

Ely,  Nevada,  steam-shovel  work,  166. 

Falls  of  rock: 

in  milling  method,  174. 

in  stoping,  185. 
Filling: 

advantages,  5,  17,  21. 

applications,  3. 

back-filling,  80,  83,  121. 

in  Homestake  mines,  121,  125,  126, 

distribution  of,  81. 

disadvantages  of  use,  4,  19,  22. 

drawing  from  stope  to  stope,  88. 

in  Combination  Mine,  66. 

in  Hecla  Mine,  68,  70. 

in  St.  Lawrence  Mine,  80. 

in  stopes,  44,  51. 

in  Tonopah  mines,  63. 

saving  in  cost,  209. 

source  of,  18. 

tendency  to  become  quick,  4. 

use,  1 8. 

waste,  17,  18. 
Finlay,  J.  R.,  186. 
Flooring,  31. 
Floors: 

boards  in  Susquehanna  Mine,  125. 

in  Broken  Hill  mines,  115. 

in  Homestake  Mine,  125. 

in  Rossland,  B.  C.,  mines,  106. 

sill,  117. 

stope,  103. 

stope  in  Homestake  mines,  121. 
Floor-boards  used  in  St.  Lawrence  Mine, 

83- 
Franklin  Mine,  85. 

Galleries  in  diamond  mines,  S.Africa,  15  2. 
Glory-holes: 

how  name  was  derived,  177. 

in  milling  method,  175. 

underground  method,  177. 
Go-devil: 

in  gravity  planes,  48. 

in  stopes,  48. 


Golden  Gate  Mine,  Utah,  89. 
Gold  Prince  Mine,  Colo.,  97,  98. 
Granby  mines,  British  Columbia: 

steam  shovel  work,  166. 
Gravity  plane  in  stopes,  48. 
Grizzly  in  glory-hole  mining,  175. 

Hand  mining: 

advantages  of,  162. 

disadvantages  of,  162. 

open-cut  work,  158,  171. 
Handling: 

back-filling  in  St.  Lawrence  Mine,  83. 

by  Chinaman  Chute,  53. 

by  go-devil,  48. 

by  gravity  plane,  48. 

conveyors  in,  46. 

economic  limit,  57. 

in  closed  stopes,  45. 

in  milling  method,  172,  173. 

in  open  stopes,  45. 

methods  of,  45. 

ore  in  Bunker  Hill-Sullivan    mines, 

ore  in  Bingham  Canyon   mines,  143, 

145- 

ore  in  Combination  Mine,  66. 

ore  in  Homestake  Mine,  123. 

ore  in  Lake  Superior  iron  mines,  138. 

ore  in  open-cuts,  handwork,  158. 

ore  in  stopes,  42,  44. 

raking,  46. 

shoveling,  46. 

the  monorail,  46. 

timber  in  Hecla  Mine,  70. 

timber  in  Lake  Superior  iron  mines, 
138- 

use  of  steel  metal  chutes,  46. 

waste  in  Bunker  Hill  mines,  115,  117. 

waste  in  Homestake  Mine,  125,  128. 

waste  in  St.  Lawrence  Mine,  83. 
Haulage- way : 

in  milling  method,  172. 
Head  boards  in  Hecla  Mine,  68. 
Hecla  Mine,  Coeur  d'Alene  district,  67. 
Heel  of  stope,  29,  43. 
Hitch  in  placing  stulls,  9. 
Holes  in  drilling: 

block,  50. 

dry,  41. 

wet,  41. 
Homestake  mines,  South  Dakota: 

advantages  of  methods  employed,  129. 

cost  of  support  in,  207,  208. 

depth  of  open-cuts,  156. 

description  of,  120. 

disadvantages  of  methods  employedj 
129. 


2I4 


INDEX 


Homestake  mines,  milling  method,  179. 
recent  method  of  mining,  126. 

Iron  Mt.  Mine,  Mo.: 
depth  of  open-cuts,  156. 

Keweenaw  Point,  Mich.,  3. 
temperatures  in  mines,  186. 

Labor: 

conditions  affecting,  187. 

costs,  189. 
Lagging: 

in  Hecla  Mine,  68,  70. 

in  Homestake  mines,  125. 

in  Lake  Superior  iron  mines,  133. 

in  Queen  Mine,  108,  no. 

in  St.  Lawrence  Mine,  80. 

in  Tonopah  Mine,  62. 

use  of,  31. 
Lake  Superior  iron  mines,  178. 

Keweenaw  Point,  186. 
Levels : 

distance  apart  in  iron  mines,  57,  59. 

distance  apart  in  Tonopah  mines,  60, 

.132- 
distance  apart  in  diamond  mines  of 

S.  Africa,  152. 

floors  in  Broken  Hill  mines,  115. 
in  Alaska-Tread  well  mines,  100,  101. 
in  Broken  Hill  mines,  112,  117,  119. 
in  Combination  Mine,  66. 
in  diamond  mines,  152. 
in  Hecla  Mine,  68. 
in  Homestake  Mine,  120,  129. 
in  Lake  Superior  iron  mines,  136. 
in  milling  method,  173. 
in  Zaruma  Mine,  78. 
intermediate,  in  diamond  mines,  152. 
sub-levels  in  Bingham  Canyon  mines, 

143- 
Longwall  stoping,  44. 

application  of,  44. 
Loss  of  ore: 

in  Combination  Mine,  67. 

in  diamond  mines,  S.  Africa,  155. 

in  Gold  Prince  Mine,  100. 

in  Homestake  mines,  129. 

Man- way: 

cribbed,  79. 

in  Broken  Hill  mines,  113. 

in  Bunker  Hill-Sullivan  Mine,  73. 

in  Lake  Superior  iron  mines,  132. 
Massive  deposits: 

stoping  in,  32. 


Mat  of  timber: 

in  Homestake  Mine,  125. 
in  Lake  Superior  iron  mines,  133. 
in  Susquehanna  Mine,  141. 
Mercur  Mine,  89,  92. 
Methods  of  Mining,  see  Mining. 
Milling: 

advantages  of,  179. 

disadvantages  of,  179. 

glory-holes,  175,  177. 

in  Bingham  Canyon  mines,  145,  179. 

in  iron  mines,  179. 

method  in  ore  mining,  172. 

number  of  pits,  174. 

ores  best  suited  to  method,  174. 

pits,  173. 

underground,  177. 
Mill-holes: 

in  glory-hole  mining,  175. 

in  Trimountain  Mine,  87. 
Mines: 

Alaska-Treadwell,  100,  104. 

Atlantic,  85. 

Baltic,  85. 

Bingham  Canyon,  141,  179. 

Broken  Hill,  Australia,  no,  119. 

Bunker  Hill-Sullivan,  72. 

Central,  Mo.,  186. 

Cceur  d'Alene,  Idaho,  67. 

Combination,  Goldfield,  Nev.,  64. 

Comstock  Lode,  3,  4,  186. 

Cripple  Creek,  208,  209. 

Diamond,  S.  Africa,  148. 

Franklin,  85. 

Golden  Gate,  89. 

Gold  Prince,  Colo.,  97,  98. 

Granby,  British  Columbia,  166. 

Hecla,  Cceur  d'Alene  district,  67. 

Homestake,  S.  Dakota,  120. 

Iron  Mt.,  Mo.,  156. 

Keweenaw  Point,  Mich.,  3. 

Lake  Superior  iron,  178. 

Mercur,  89,  92. 

Queen,  Negaunee,  106,  107. 

Quincy,  85. 

St.  Laurence,  Butte,  Mont.,  80. 

Susquehanna,  Minn.,  139. 

Tonopah,  Nev.,  60. 

Trimountain,  85. 

Zaruma,  S.  America,  77,  79,  115. 
Mining: 

advantages  of  stull    method,   Tono- 
pah Mine,  63. 

back-filling,  St.  Lawrence  Mine,  84. 

by  filling,  77. 

by  hand,  in  open-cuts,  158,  160,  162. 

by  scrapers,  163. 

by  steam  shovels,  167, 


INDEX 


215 


Mining: 
caving: 

in  diamond  mines,  148,  152. 

in  Mercur  mines,  89. 

in  Michigan  iron  mines,  132. 

methods,  148. 
disadvantages  of  stull  method,  Tono- 

pah  Mine,  64. 
filling,  184. 

in  copper  mines,  Lake  Superior,  85. 
Glory-hole  methods,  175. 
Gold  Prince  Mine,  98. 
in  Alaska-Treadwell  mines,  100,  104. 
in  bedded  deposits  with  props,  56. 
inclined  floors,  73. 
iron  mines,  Birmingham,  Ala.,  56. 
methods,  55,  56. 
milling  method,  172. 
open-cut  mining,  157. 
over-hand   stoping   in    Combination 

Mine,  66. 

rill  stoping  in  Zaruma  Mine,  80. 
room-and- pillar,  57. 
square-set  method,  Rossland,  B.  C., 

104. 
sub-drift  method  of,  89. 

in  diamond  mines,  152,  154. 

in  Lake  Superior  iron  mines,  132, 

135,  141- 

top-slice  method,  132. 
Mixing  of  ore  and  waste,  146. 
Mud  rushes  in  diamond  mines,  S.  Africa, 
155- 

Open  cut: 

advantages  of,  180, 181. 

Alaska-Treadwell  mines,  Alaska,  156. 

by  steam  shovels,  166. 

depth  of,  156. 

diamond  mines,  S.  Africa,  156. 

disadvantages  of,  180,  181. 

Glory -hole  mining,  157,  177. 

Homestake  mines,  S.  D.,  156. 

in  diamond  mines,  148. 

Iron  Mountain  Mine,  Mo.,  156. 

keeping  separate,  ore  and  waste,  177. 

mining  in  general,  156. 

Rio  Tinto  mines,  Spain,  156. 
Open-stope  method  of  mining,  112. 

in  Broken  Hill  mines,  113. 
Ore  pockets,  stopes  in  Homestake  mines, 

128. 
Ore  reserve,  17,  27,  40,  41,  98. 

advantages  of,  209. 

in  Gold  Prince  Mine,  98,  100. 

in  stoping,  209. 
Ore,  hard  and  soft  iron,  57,  59. 

suited  to  steam-shovel  work,  168. 


Overburden: 

maximum  and   minimum  thickness, 
167. 

removal  of,  by  steam  shovel,  166. 
Overhand  stoping: 

advantages  of,  40. 

application,  39. 

conditions  affecting  working,  26. 

disadvantages  of,  40. 

in  Bunker  Hill-Sullivan  Mine,  73. 

in  Combination  Mine,  64. 

in  Hecla  Mine,   Cceur  d'Alene  dis- 
trict, 68. 

in  milling  method,  172,  174,  178. 

in  Tonopah  Mine,  60. 

in  Zaruma  Mine,  S.  America,  78. 

method,  25. 

method  of  attack,  25. 

Pack-walls: 

Trimountain  Mine,  88. 
Pentices  in  Alaska-Treadwell  mines,  103. 
Percentage  method  of  calculating  costs, 

191,  192. 

Pickers  in  Trimountain  Mine,  87. 
Pillar-and-stope  method  of  mining,  112. 
Pillar-drawing: 

in  Bingham  Canyon  mines,  145. 

in  Broken  Hill  mines,  118. 

in  diamond  mines,  S.  Africa,  152. 

in  Homestake  mines,  126,  129. 

in  iron  mines,  57. 

in  Lake  Superior  iron  mines,  133,  138. 

in  Mercur  mines,  91. 

in  milling  method,  178. 

in  Queen  Mine,  108,  no. 

in  sub-drift  system,  138. 

in  Susquehanna  Mine,  139. 
Pillars: 

advantages  of  use,  20. 

arch,  7,  32,  124. 

dead-ends,  37. 

distance  between,  104. 

drawing,  57,  100,  117,  126,  138,  145, 
152,  178. 

failure  of,  7. 

forms  of,  7. 

in  Alaska-Treadwell  mines,  100. 

in  British  Columbia  mines,  143. 

in  Gold  Prince  Mine,  97. 

in  Lake  Superior  iron  mines,  136. 

in  sub-drift  method  of  mining,  136. 

irregularity  in  forming  and  placing,  7. 

lacing  in  Homestake  mines,  128. 

objection  to  use  of,  6. 

pentices  in  Alaska-Treadwell  mines, 
103. 

robbing  of,  178. 


2l6 


INDEX 


Pillars: 
shaft,  37,  57- 
sheet,  in  Alaska-Treadwell  mines,  103. 
size  of,  7. 

stump  in  Gold  Prince  Mine,  98. 
stump   in   Bingham   Canyon   mines, 

145- 

wall,  36. 

weakening  by  undercutting  in  Home- 
stake  mines,  126. 
Pipes  or  ducts,  in  diamond  mines,  148, 

149. 
Porphyry  copper  ore,  Bingham  Canyon, 

143- 

Power,  in  stoping,  188,  190. 
Props: 

advantages  of,  20. 

disadvantages  of,  20. 

distance  apart  in  iron  mines,  59. 

in  mining  iron  ore,  56. 

in  St.  Lawrence  Mine,  Butte,  Mont.. 

83- 

methods  of  setting,  8. 
size  in  iron  mines,  59. 
Posts: 

advantages  of,  20. 
disadvantages  of,  20. 
in  the  Mercur  Mine,  92. 
in  Zaruma  Mine,  78. 
methods  of  setting,  8. 
with  stull-sets,  68. 

Quarry,  open-cut  work,  161. 
Queen  Mine,  Negaunee,  106,  107. 
Quincy,  Mine,  85. 

Raises: 

chute,  97,  101. 

in  Alaska-Treadwell  Mine,  101. 

for  ventilation,  101. 

in  Alaska-Treadwell  mines,  101. 

in  Bingham  Canyon  mines,  143,  146. 

in  Glory-hole  mining,  175. 

in  Homestake  mines,  123,,  128. 

in  Lake  Superior  iron  mines,  132,  133. 

in  milling  method,  173. 

in  stoping,  32,  33,  34. 

main,  101. 

use  of,  in  stoping,  78,  81. 
Raking  ore  in  stopes,  46. 
Resiling,  38. 

application  of,  43. 
Rill  stoping: 

advantages  of,  80. 

designation,  80. 

disadvantages  of,  80. 

in  Broken  Hill  mines,  115. 

in  diamond  mines,  S.  Africa,  153,  154. 


Rill  stoping: 

in  Trimountain  and  Baltic  mines,  86. 

in  Zaruma  mines,  77. 
Rock  walls: 

in  copper  mines,  85. 
Roof  of  galleries  in  diamond  mines  of 

S.  Africa,  152. 
Room  and  pillar  working: 

in  Alaska-Treadwell  Mine,  100. 

in  Bunker  Hill  Mine,  117. 

in  Homestake  Mine,  126. 

in  iron  mines,  Birmingham,  Ala.,  57. 

in  Lake  Superior  iron  mines,  138. 

Scraper: 

advantages  of,  165. 

disadvantages  of,  165. 

drag  in  open-cut  working,  163. 

in  open-cut  working,  157,  163. 
Shaft  pillars,  7. 

in  iron  mines,  57. 
Sheet-pillars: 

in  Alaska-Treadwell  mines,  103. 
Shoveling: 

in  Homestake  mines,  125,  128. 

in  Lake  Superior  iron  mines,  138. 

in  open-cut  work,  hand  mining,  60. 

in  stopes,  46. 

in  Susquehanna  iron  mine,  139. 
Shovelers: 

in  Homestake  mines,  125. 
Shrinkage  stoping: 

description  of,  27. 

in  Alaska-Treadwell  mines,  103. 

in  Broken  Hill  mines,  117. 

in  Gold  Prince  Mine,  97. 

in  Homestake  Mine,  125. 
Side  stoping: 

application,  44. 

objection  to  use,  44. 
Side-swiping  in  Mercur  Mine,  91. 
Slices: 

inclined,  in  Broken  Hill  mines,  115. 

in  Zaruma  Mine,  78. 
Sorting: 

in  Hecla  Mine,  68. 

in  open-cut  work,  182. 

in  Trimountain 'Mine,  88. 

in  Zaruma  Mine,  80. 

of  ore,  182. 

in  Trimountain  Mine,  87. 

of  waste  in  stoping,  39,  42. 
Spread  of  costs,  190,  197,  198,  202,  203. 
Square-sets : 

advantages  of,  21,  112. 

application  of,  77. 

cause  of  failure,  15. 

cost  of,  in  Homestake  mines,  207,  208. 


INDEX 


217 


Square-sets : 

economy  of  use,  17,  95,  113. 

framing  of,  13. 

in  British  Columbia  mines,  106. 

in  Broken  Hill  mines,  112,  117. 

in  Comstock  mines,  4. 

in  Coeur  d'Alene  mines,  72. 

in  Homestake  mines,  120,  128. 

in  Queen  Mine,  Negaunee,  Mich.,  108. 

in  Rossland,  B.  C.,  mines,  104. 

in  St.  Lawrence  Mine,  80. 

in  Tonopah  mines,  60. 

method  of  placing,  12,  13. 

parts  of,  12. 

size  of,  in  Bunker  Hill-Sullivan  mines, 

73- 

size  and  length  of  posts,  13,  15. 

size  of,  in  Rossland,  B.  C.,  mines,  106. 

use  of  parts  of  sets,  13. 

used  with  stulls,  10. 

when  applicable,  12,  95. 

with  round  timber,  in  Rossland  mines, 

106. 
Steam-shovel  work: 

advantages  of,  171. 

broken-boom,  171. 

description  of,  141. 

development  of,  168. 

disadvantages  of,  172. 

in  milling  method,  174. 

in  open-cut  work,  157. 

in  phosphate  mining,  171. 

loading  stock  piles,  169. 

methods  of,  167,  169. 

operation,  168,  169. 

when  applicable,  171. 
Stock  piles,  169,  171. 
St.  Lawrence  Mine,  Butte,  Mont.,  80. 
Sloping: 

back,  68. 

beginning   of   underhand   and   over- 
hand, 32. 

breast,  36,  37,  42,  48,  59,  114. 

classification  of  methods,  24. 

combined,  34,  43. 

conditions  affecting  choice  of  method, 
24. 

Cornish  system,  30. 

cost  of,  183,  189. 

cutting-out,  27,  29,  37,  64,  87,  103, 
194. 

drift,  29,  194. 

in  Bunker  Hill-Sullivan  mines,  75. 

in  Broken  Hill  mines,  115,  119. 

in  Gold  Prince  Mine,  Colo.,  97. 

influence  of  character  of  walls  and  ore, 
25. 

influence  of  dip,  24. 


Stoping: 

influence  of  handling  ore  in  stopes,  25. 
in  Queen  Mine,  Mich.,  108. 
longwall,  38,  43,  44. 
methods  of,  23. 
overhand,  25,  29,  31,  32,  34,  37,  38, 

39,   59,   60,   64,   68,    73,  78,    106, 

153,  172,  174,  178. 
powder  used,  195. 
practice  in  the  United  States,  29 
raise,  37,  194. 
rate  of,  195. 
rill,  in  Broken  Hill  mines,  115. 

in  diamond  mines,   South  Africa, 
153,154. 

in  Trimountain  and  Baltic  mines, 
86. 

in  Zaruma  mines,  80,  153. 
shrinkage,  27,  97,  103,  117,  125. 
side,  37,  38,  43 ,44. 

in  Mercur  mines,  91. 
underhand,  30,  31,  32,  34. 
where  ore  occurs  in  stringers,  27. 
where  ore  is  of  uniform  value,  27. 
Stopes : 

back,  29,  103,  123. 
back  of,  43,  70. 

circular,  in  milling   method,   under- 
ground, 178. 
closed,  45,  50. 
collapse  of  large,  178. 
drift,  29,  101. 

floors    in     Alaska-Treadwell    mines, 
103,  184. 

in  Queen  Mine,  Mich.,  108. 
handling  in,  36. 
heel  of,  29,  43. 
height  in  Broken  Hill  mines,  118. 

in  Homestake  mines,  123. 
height  of,  64,  104. 
in  Broken  Hill  mines,  117. 
in  diamond  mines,  South  Africa,  153. 
in  Homestake  mines,  121,  184. 
in  iron  mines,  57. 
in  St.  Lawrence  Mine,  81. 
in  Tonopah  mines,  60,  62,  63. 
open,  45. 
opening  of,  27. 

opening  of,  in  diamond  mines,  153. 
opening  of  underhand,  32. 
ore  pockets  in  Homestake  mines,  128. 
raise,  27. 
stope  faces,  108. 
toe  of,  29. 

width  of,  in  Homestake  mines,  123. 
Strip-pits : 
drainage  in,  165. 
increase  of  size  by  wheel  scrapers,  165. 


2l8 


INDEX 


Strip-pits: 

in  working  coal,  165. 

size  of,  163. 
Stripping: 

as  applied  to  removal  of  pillars,  138. 

in  open-cut  mining,  157,  163,  164. 

in  stoping,  39. 

pits,  163. 
Stull: 

floors,  36,  40. 

headings  in  Tonopah  Mine,  62. 
in  Hecla  Mine,  68. 

in  Tonopah  Mine,  62. 
Stull-set  mining: 

advantages  of,  72. 

disadvantages  of,  72. 

in  Hecla  Mine,  67,  68. 
Stulls: 

advantages  of,  21. 

angle  of  underlie,  9. 

battery  of,  10. 

disadvantages  of,  21. 

in  Cceur  d'Alene  mines,  68. 

in  Combination  Mine,  66. 

in  Michigan  mines,  3. 

in  St.  Lawrence  Mine,  80. 

in  Tonopah  mines,  60,  62,  63. 

lagged,  43. 

method  of  placing,  9. 

waste,  10. 

when  placed,  10. 

winged,  50. 

with  props,  10. 

with  square-sets,  10. 
Stull-floors,  40. 
Stull-set,  Hecla  Mine,  68. 
Sub-drifts: 

advantages  of,  94. 

blind,  in  Alaska-Treadwill  mines,  101. 

disadvantages  of,  94. 

distance    apart    in   diamond   mines, 
152. 

height  of,  Lake  Superior  iron  mines, 
136,  138. 

in  Alaska-Tread  well  mines,  101,  103. 

in  Bingham  Canyon  mines,  145. 

in  diamond  mines,  152. 

in  Lake  Superior  iron  mines,  132,  135, 
136,  138. 

in  Mercur  mines,  89,  91. 

in  Queen  Mine,  Negaunee,  Mich.,  106. 

method  of  mining,  135. 
advantages  of,  141. 
disadvantages  of,  141. 
in  Susquehanna  Mine,  Minn.,  139. 
Support : 

by  filling,  77,  78. 

by  stull-sets,  67. 


Support: 

cost  of,  28,  184,  207. 

cost  of  square-sets,  207,  208. 

indirect  methods,  6,  19. 

methods  of,  5,  6. 

ore  in  stopes,  27. 

pillars  of  ore  or  waste,  6. 

square-sets,  4,  10,  12,  13,  21. 

support  of  ore  in  stopes,  27. 
Supplies  in  stoping,  188,  190. 
Susquehanna  Mine,  Minn.,  139. 

Temperatures  in  mining,  186. 
Terraces: 

in  diamond  mines  of  S.  Africa,  154. 

in  iron  mines,  138. 

in  open-cut  work,  160. 

in  steam-shovel  work,  169. 
Test  pits,  proving  deposits,  168. 
Tight  corner  in  stoping,  36,  44. 
Timber: 

A-form  in  Queen  Mine,  108. 

Cantilever  supports,  115. 

Corduroy,  3. 

Cribs,  6,  12,  114,  115. 

economy  in  use  of,  Homestake  Mine, 
126. 

for  mine  use,  8. 

handling  of,  70. 

in  diamond  mines,  152. 

in  Homestake  mines,  121. 

in  Lake  Superior  iron  mines,  139. 

kinds  of,  8. 

lacing  in  Homestake  mines,  128. 

props,  6. 

scarcity  of,  8. 

size  of: 

in  Rossland,  B.  C.,  mines,  106. 
in  Susquehanna  Mine,  139. 
in  Tonopah  Mine,  62. 

slides  in  Hecla  Mine,  70. 

square-sets,  4,  10,  12,  13,  15,  17,  21, 
60. 

use  of  broken,  126. 

use  of,  with  caving,  5. 

wall-pieces     in    Trimountain    Mine, 

87- 

Toe  of  stope,  29. 
Ton-day  method  of  calculating  costs, 

191,  192. 

Tonopah  Mine,  Nev.,  60. 
Top-slice  method  of  mining,  132,  135. 
advantages  of,  135. 
disadvantages  of,  135. 
Trammers,  87. 
Trimountain  Mine,  85. 
Tunnels  in  diamond  mines,  S.  Africa, 
152. 


INDEX 


219 


Underhand  sloping: 
advantages  of,  41. 
application  of,  41. 
disadvantages  of,  41. 
in  milling  method,  174,  178. 

Ventilation: 

in  Bingham  Canyon  mines,  143. 
in  Combination  Mine,  67. 
in  diamond  mines,  S.  Africa,  155. 
in  mines,  186. 
in  Tonopah  Mine,  63. 
raises  for,  in  Alaska-Treadwell  mines, 
101,  103. 

Wages,  189. 

Wall-pieces  in  Baltic  and  Trimountain 
mines,  87. 


Wall  pillars,  7. 

Waste  bank,  open-cut  work,  165. 

Wheelbarrows: 

use  in  stopes,  44,  54. 

use  in  top-slice  method,  iron  mines, 

133- 

Winged  stulls,  see  Stulls,  50,  51. 
Winzes: 

in  Cceur  d'Alene  mines,  73. 

in  St.  Lawrence  mines,  Butte,  81. 
Woods,  see  Timber,  8. 


Yates,  B.  C.,  207. 


Zaruma  Mine,  South  America,  77,  79, 


M127048 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


